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 $52.91   9.538%   $57.9566   $57.96   $57.95   $58.00  
  Purchase #2 $11.43   8.572%   $12.4098   $12.41   $12.40   $12.40  
  Purchase #3 $170.78   11.474%   $190.3753   $190.38   $190.40   $190.40  
  Purchase #4 $45.43   7.170%   $48.6873   $48.69   $48.70   $48.70  
  Purchase #5 $195.46   5.277%   $205.7744   $205.77   $205.75   $205.80  
  Purchase #6 $69.42   4.132%   $72.2884   $72.29   $72.30   $72.30  
  Purchase #7 $173.76   11.653%   $194.0083   $194.01   $194.00   $194.00  
  7 purchase totals = $719.19       $781.5001   $781.51   $781.50   $781.60