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 $181.70   6.797%   $194.0501   $194.05   $194.05   $194.10  
  Purchase #2 $226.71   9.686%   $248.6691   $248.67   $248.65   $248.70  
  Purchase #3 $58.63   10.362%   $64.7052   $64.71   $64.70   $64.70  
  Purchase #4 $250.81   10.775%   $277.8348   $277.83   $277.85   $277.80  
  Purchase #5 $64.38   13.577%   $73.1209   $73.12   $73.10   $73.10  
  Purchase #6 $189.90   8.321%   $205.7016   $205.70   $205.70   $205.70  
  Purchase #7 $76.66   5.582%   $80.9392   $80.94   $80.95   $80.90  
  7 purchase totals = $1,048.79       $1,145.0209   $1,145.02   $1,145.00   $1,145.00