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 $72.25   13.674%   $82.1295   $82.13   $82.15   $82.10  
  Purchase #2 $55.96   13.111%   $63.2969   $63.30   $63.30   $63.30  
  Purchase #3 $43.37   12.218%   $48.6689   $48.67   $48.65   $48.70  
  Purchase #4 $128.53   13.590%   $145.9972   $146.00   $146.00   $146.00  
  Purchase #5 $131.66   11.306%   $146.5455   $146.55   $146.55   $146.50  
  Purchase #6 $236.77   5.354%   $249.4467   $249.45   $249.45   $249.40  
  Purchase #7 $60.38   4.696%   $63.2154   $63.22   $63.20   $63.20  
  7 purchase totals = $728.92       $799.3001   $799.32   $799.30   $799.20