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 $227.32   11.601%   $253.6914   $253.69   $253.70   $253.70  
  Purchase #2 $194.96   13.526%   $221.3303   $221.33   $221.35   $221.30  
  Purchase #3 $237.99   9.748%   $261.1893   $261.19   $261.20   $261.20  
  Purchase #4 $93.88   8.809%   $102.1499   $102.15   $102.15   $102.10  
  Purchase #5 $187.52   13.632%   $213.0827   $213.08   $213.10   $213.10  
  Purchase #6 $110.33   8.660%   $119.8846   $119.88   $119.90   $119.90  
  Purchase #7 $137.75   5.391%   $145.1761   $145.18   $145.20   $145.20  
  7 purchase totals = $1,189.75       $1,316.5043   $1,316.50   $1,316.60   $1,316.50