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 $48.83   11.291%   $54.3434   $54.34   $54.35   $54.30  
  Purchase #2 $177.75   7.778%   $191.5754   $191.58   $191.60   $191.60  
  Purchase #3 $33.34   13.702%   $37.9082   $37.91   $37.90   $37.90  
  Purchase #4 $146.50   5.450%   $154.4843   $154.48   $154.50   $154.50  
  Purchase #5 $145.92   4.777%   $152.8906   $152.89   $152.90   $152.90  
  Purchase #6 $116.48   7.542%   $125.2649   $125.26   $125.25   $125.30  
  Purchase #7 $215.79   9.519%   $236.3311   $236.33   $236.35   $236.30  
  7 purchase totals = $884.61       $952.7979   $952.79   $952.85   $952.80