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 $159.82   10.132%   $176.013   $176.01   $176.00   $176.00  
  Purchase #2 $120.73   9.355%   $132.0243   $132.02   $132.00   $132.00  
  Purchase #3 $88.75   10.782%   $98.319   $98.32   $98.30   $98.30  
  Purchase #4 $209.51   7.618%   $225.4705   $225.47   $225.45   $225.50  
  Purchase #5 $68.54   13.658%   $77.9012   $77.90   $77.90   $77.90  
  Purchase #6 $68.50   10.579%   $75.7466   $75.75   $75.75   $75.70  
  Purchase #7 $164.54   5.422%   $173.4614   $173.46   $173.45   $173.50  
  7 purchase totals = $880.39       $958.9360   $958.93   $958.85   $958.90