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 $58.25   7.729%   $62.7521   $62.75   $62.75   $62.80  
  Purchase #2 $187.54   10.838%   $207.8656   $207.87   $207.85   $207.90  
  Purchase #3 $248.68   5.234%   $261.6959   $261.70   $261.70   $261.70  
  Purchase #4 $6.39   3.868%   $6.6372   $6.64   $6.65   $6.60  
  Purchase #5 $197.95   6.589%   $210.9929   $210.99   $211.00   $211.00  
  Purchase #6 $66.52   10.661%   $73.6117   $73.61   $73.60   $73.60  
  Purchase #7 $125.93   7.377%   $135.2199   $135.22   $135.20   $135.20  
  7 purchase totals = $891.26       $958.7753   $958.78   $958.75   $958.80