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 $67.28   13.143%   $76.1226   $76.12   $76.10   $76.10  
  Purchase #2 $129.25   10.107%   $142.3133   $142.31   $142.30   $142.30  
  Purchase #3 $193.48   4.622%   $202.4226   $202.42   $202.40   $202.40  
  Purchase #4 $30.95   7.439%   $33.2524   $33.25   $33.25   $33.30  
  Purchase #5 $184.53   6.779%   $197.0393   $197.04   $197.05   $197.00  
  Purchase #6 $133.85   10.793%   $148.2964   $148.30   $148.30   $148.30  
  Purchase #7 $59.84   4.464%   $62.5113   $62.51   $62.50   $62.50  
  7 purchase totals = $799.18       $861.9579   $861.95   $861.90   $861.90