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 $60.83   8.733%   $66.1423   $66.14   $66.15   $66.10  
  Purchase #2 $233.47   13.567%   $265.1449   $265.14   $265.15   $265.10  
  Purchase #3 $169.68   11.263%   $188.7911   $188.79   $188.80   $188.80  
  Purchase #4 $236.97   10.748%   $262.4395   $262.44   $262.45   $262.40  
  Purchase #5 $63.48   13.758%   $72.2136   $72.21   $72.20   $72.20  
  Purchase #6 $35.42   9.281%   $38.7073   $38.71   $38.70   $38.70  
  Purchase #7 $242.26   9.171%   $264.4777   $264.48   $264.50   $264.50  
  7 purchase totals = $1,042.11       $1,157.9164   $1,157.91   $1,157.95   $1,157.80