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 $112.87   8.604%   $122.5813   $122.58   $122.60   $122.60  
  Purchase #2 $177.40   4.418%   $185.2375   $185.24   $185.25   $185.20  
  Purchase #3 $59.37   5.463%   $62.6134   $62.61   $62.60   $62.60  
  Purchase #4 $30.80   10.297%   $33.9715   $33.97   $33.95   $34.00  
  Purchase #5 $226.99   9.791%   $249.2146   $249.21   $249.20   $249.20  
  Purchase #6 $49.47   8.799%   $53.8229   $53.82   $53.80   $53.80  
  Purchase #7 $144.71   11.843%   $161.848   $161.85   $161.85   $161.80  
  7 purchase totals = $801.61       $869.2892   $869.28   $869.25   $869.20