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 $44.91   11.263%   $49.9682   $49.97   $49.95   $50.00  
  Purchase #2 $57.76   8.316%   $62.5633   $62.56   $62.55   $62.60  
  Purchase #3 $187.30   11.728%   $209.2665   $209.27   $209.25   $209.30  
  Purchase #4 $240.75   11.521%   $268.4868   $268.49   $268.50   $268.50  
  Purchase #5 $25.78   4.716%   $26.9958   $27.00   $27.00   $27.00  
  Purchase #6 $159.80   11.695%   $178.4886   $178.49   $178.50   $178.50  
  Purchase #7 $93.63   3.403%   $96.8162   $96.82   $96.80   $96.80  
  7 purchase totals = $809.93       $892.5854   $892.60   $892.55   $892.70