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 $54.78   13.250%   $62.0384   $62.04   $62.05   $62.00  
  Purchase #2 $77.72   8.206%   $84.0977   $84.10   $84.10   $84.10  
  Purchase #3 $216.83   9.262%   $236.9128   $236.91   $236.90   $236.90  
  Purchase #4 $91.70   10.119%   $100.9791   $100.98   $101.00   $101.00  
  Purchase #5 $68.27   8.575%   $74.1242   $74.12   $74.10   $74.10  
  Purchase #6 $206.33   7.199%   $221.1837   $221.18   $221.20   $221.20  
  Purchase #7 $106.80   11.806%   $119.4088   $119.41   $119.40   $119.40  
  7 purchase totals = $822.43       $898.7447   $898.74   $898.75   $898.70