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 $60.92   8.421%   $66.0501   $66.05   $66.05   $66.10  
  Purchase #2 $162.94   4.309%   $169.9611   $169.96   $169.95   $170.00  
  Purchase #3 $178.51   12.643%   $201.079   $201.08   $201.10   $201.10  
  Purchase #4 $229.80   11.795%   $256.9049   $256.90   $256.90   $256.90  
  Purchase #5 $208.96   7.859%   $225.3822   $225.38   $225.40   $225.40  
  Purchase #6 $112.71   8.192%   $121.9432   $121.94   $121.95   $121.90  
  Purchase #7 $10.84   10.243%   $11.9503   $11.95   $11.95   $12.00  
  7 purchase totals = $964.68       $1,053.2708   $1,053.26   $1,053.30   $1,053.40