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 $152.42   8.429%   $165.2675   $165.27   $165.25   $165.30  
  Purchase #2 $172.39   12.444%   $193.8422   $193.84   $193.85   $193.80  
  Purchase #3 $70.95   3.711%   $73.583   $73.58   $73.60   $73.60  
  Purchase #4 $237.35   12.439%   $266.874   $266.87   $266.85   $266.90  
  Purchase #5 $41.41   11.843%   $46.3142   $46.31   $46.30   $46.30  
  Purchase #6 $63.98   12.174%   $71.7689   $71.77   $71.75   $71.80  
  Purchase #7 $41.78   13.758%   $47.5281   $47.53   $47.55   $47.50  
  7 purchase totals = $780.28       $865.1779   $865.17   $865.15   $865.20