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 $55.74   11.605%   $62.2086   $62.21   $62.20   $62.20  
  Purchase #2 $147.30   11.472%   $164.1983   $164.20   $164.20   $164.20  
  Purchase #3 $66.85   6.370%   $71.1083   $71.11   $71.10   $71.10  
  Purchase #4 $132.83   10.197%   $146.3747   $146.37   $146.35   $146.40  
  Purchase #5 $153.66   9.269%   $167.9027   $167.90   $167.90   $167.90  
  Purchase #6 $245.39   11.651%   $273.9804   $273.98   $274.00   $274.00  
  Purchase #7 $26.65   12.344%   $29.9397   $29.94   $29.95   $29.90  
  7 purchase totals = $828.42       $915.7127   $915.71   $915.70   $915.70