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 $155.49   7.799%   $167.6167   $167.62   $167.60   $167.60  
  Purchase #2 $94.79   3.674%   $98.2726   $98.27   $98.25   $98.30  
  Purchase #3 $60.58   10.399%   $66.8797   $66.88   $66.90   $66.90  
  Purchase #4 $107.88   6.873%   $115.2946   $115.29   $115.30   $115.30  
  Purchase #5 $85.46   3.284%   $88.2665   $88.27   $88.25   $88.30  
  Purchase #6 $174.59   9.733%   $191.5828   $191.58   $191.60   $191.60  
  Purchase #7 $46.62   11.579%   $52.0181   $52.02   $52.00   $52.00  
  7 purchase totals = $725.41       $779.9310   $779.93   $779.90   $780.00