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 $46.73   8.550%   $50.7254   $50.73   $50.75   $50.70  
  Purchase #2 $58.95   12.532%   $66.3376   $66.34   $66.35   $66.30  
  Purchase #3 $182.46   7.123%   $195.4566   $195.46   $195.45   $195.50  
  Purchase #4 $78.27   8.829%   $85.1805   $85.18   $85.20   $85.20  
  Purchase #5 $90.86   3.104%   $93.6803   $93.68   $93.70   $93.70  
  Purchase #6 $155.34   3.651%   $161.0115   $161.01   $161.00   $161.00  
  Purchase #7 $45.43   3.790%   $47.1518   $47.15   $47.15   $47.20  
  7 purchase totals = $658.04       $699.5437   $699.55   $699.60   $699.60