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 $118.55   12.228%   $133.0463   $133.05   $133.05   $133.00  
  Purchase #2 $153.96   7.126%   $164.9312   $164.93   $164.95   $164.90  
  Purchase #3 $110.55   7.738%   $119.1044   $119.10   $119.10   $119.10  
  Purchase #4 $62.38   12.768%   $70.3447   $70.34   $70.35   $70.30  
  Purchase #5 $153.79   12.576%   $173.1306   $173.13   $173.15   $173.10  
  Purchase #6 $26.84   6.633%   $28.6203   $28.62   $28.60   $28.60  
  Purchase #7 $56.34   7.807%   $60.7385   $60.74   $60.75   $60.70  
  7 purchase totals = $682.41       $749.9160   $749.91   $749.95   $749.70