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 $54.45   8.795%   $59.2389   $59.24   $59.25   $59.20  
  Purchase #2 $233.71   7.378%   $250.9531   $250.95   $250.95   $251.00  
  Purchase #3 $63.50   7.398%   $68.1977   $68.20   $68.20   $68.20  
  Purchase #4 $94.27   6.621%   $100.5116   $100.51   $100.50   $100.50  
  Purchase #5 $186.62   12.589%   $210.1136   $210.11   $210.10   $210.10  
  Purchase #6 $186.49   7.517%   $200.5085   $200.51   $200.50   $200.50  
  Purchase #7 $108.37   8.614%   $117.705   $117.71   $117.70   $117.70  
  7 purchase totals = $927.41       $1,007.2284   $1,007.23   $1,007.20   $1,007.20