Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $79.79   8.582%   $86.6376   $86.64   $86.65   $86.60  
  Purchase #2 $220.58   12.747%   $248.6973   $248.70   $248.70   $248.70  
  Purchase #3 $130.34   12.517%   $146.6547   $146.65   $146.65   $146.70  
  Purchase #4 $128.83   10.711%   $142.629   $142.63   $142.65   $142.60  
  Purchase #5 $136.53   5.489%   $144.0241   $144.02   $144.00   $144.00  
  Purchase #6 $189.80   6.872%   $202.8431   $202.84   $202.85   $202.80  
  Purchase #7 $47.90   5.663%   $50.6126   $50.61   $50.60   $50.60  
  7 purchase totals = $933.77       $1,022.0984   $1,022.09   $1,022.10   $1,022.00