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 $56.74   10.848%   $62.8952   $62.90   $62.90   $62.90  
  Purchase #2 $117.75   13.317%   $133.4308   $133.43   $133.45   $133.40  
  Purchase #3 $22.52   7.675%   $24.2484   $24.25   $24.25   $24.20  
  Purchase #4 $133.95   9.199%   $146.2721   $146.27   $146.25   $146.30  
  Purchase #5 $56.53   7.648%   $60.8534   $60.85   $60.85   $60.90  
  Purchase #6 $71.40   13.532%   $81.0618   $81.06   $81.05   $81.10  
  Purchase #7 $191.97   13.263%   $217.431   $217.43   $217.45   $217.40  
  7 purchase totals = $650.86       $726.1927   $726.19   $726.20   $726.20