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 $231.27   13.241%   $261.8925   $261.89   $261.90   $261.90  
  Purchase #2 $178.30   13.140%   $201.7286   $201.73   $201.75   $201.70  
  Purchase #3 $77.56   9.547%   $84.9647   $84.96   $84.95   $85.00  
  Purchase #4 $237.60   8.502%   $257.8008   $257.80   $257.80   $257.80  
  Purchase #5 $131.84   13.572%   $149.7333   $149.73   $149.75   $149.70  
  Purchase #6 $65.46   12.324%   $73.5273   $73.53   $73.55   $73.50  
  Purchase #7 $148.30   5.219%   $156.0398   $156.04   $156.05   $156.00  
  7 purchase totals = $1,070.33       $1,185.6870   $1,185.68   $1,185.75   $1,185.60