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 $61.58   13.693%   $70.0121   $70.01   $70.00   $70.00  
  Purchase #2 $184.95   8.428%   $200.5376   $200.54   $200.55   $200.50  
  Purchase #3 $64.94   3.767%   $67.3863   $67.39   $67.40   $67.40  
  Purchase #4 $62.25   11.327%   $69.3011   $69.30   $69.30   $69.30  
  Purchase #5 $157.39   7.450%   $169.1156   $169.12   $169.10   $169.10  
  Purchase #6 $249.28   3.674%   $258.4385   $258.44   $258.45   $258.40  
  Purchase #7 $130.29   6.855%   $139.2214   $139.22   $139.20   $139.20  
  7 purchase totals = $910.68       $974.0126   $974.02   $974.00   $973.90