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 $85.54   13.562%   $97.1409   $97.14   $97.15   $97.10  
  Purchase #2 $64.43   5.123%   $67.7307   $67.73   $67.75   $67.70  
  Purchase #3 $84.75   9.685%   $92.958   $92.96   $92.95   $93.00  
  Purchase #4 $127.47   5.842%   $134.9168   $134.92   $134.90   $134.90  
  Purchase #5 $194.58   6.602%   $207.4262   $207.43   $207.45   $207.40  
  Purchase #6 $197.28   5.316%   $207.7674   $207.77   $207.75   $207.80  
  Purchase #7 $142.59   12.417%   $160.2954   $160.30   $160.30   $160.30  
  7 purchase totals = $896.64       $968.2354   $968.25   $968.25   $968.20