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 $60.46   9.231%   $66.0411   $66.04   $66.05   $66.00  
  Purchase #2 $241.67   13.584%   $274.4985   $274.50   $274.50   $274.50  
  Purchase #3 $49.53   7.519%   $53.2542   $53.25   $53.25   $53.30  
  Purchase #4 $125.42   13.158%   $141.9228   $141.92   $141.90   $141.90  
  Purchase #5 $59.25   12.256%   $66.5117   $66.51   $66.50   $66.50  
  Purchase #6 $248.74   5.650%   $262.7938   $262.79   $262.80   $262.80  
  Purchase #7 $120.69   7.360%   $129.5728   $129.57   $129.55   $129.60  
  7 purchase totals = $905.76       $994.5949   $994.58   $994.55   $994.60