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 $92.38   10.727%   $102.2896   $102.29   $102.30   $102.30  
  Purchase #2 $177.90   9.823%   $195.3751   $195.38   $195.40   $195.40  
  Purchase #3 $137.50   8.744%   $149.523   $149.52   $149.50   $149.50  
  Purchase #4 $80.82   4.188%   $84.2047   $84.20   $84.20   $84.20  
  Purchase #5 $204.41   5.760%   $216.184   $216.18   $216.20   $216.20  
  Purchase #6 $193.90   11.320%   $215.8495   $215.85   $215.85   $215.80  
  Purchase #7 $237.45   10.211%   $261.696   $261.70   $261.70   $261.70  
  7 purchase totals = $1,124.36       $1,225.1219   $1,225.12   $1,225.15   $1,225.10