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 $57.36   11.684%   $64.0619   $64.06   $64.05   $64.10  
  Purchase #2 $224.73   12.628%   $253.1089   $253.11   $253.10   $253.10  
  Purchase #3 $93.40   13.436%   $105.9492   $105.95   $105.95   $105.90  
  Purchase #4 $139.43   9.389%   $152.5211   $152.52   $152.50   $152.50  
  Purchase #5 $243.27   10.565%   $268.9715   $268.97   $268.95   $269.00  
  Purchase #6 $237.96   11.855%   $266.1702   $266.17   $266.15   $266.20  
  Purchase #7 $224.38   8.294%   $242.9901   $242.99   $243.00   $243.00  
  7 purchase totals = $1,220.53       $1,353.7729   $1,353.77   $1,353.70   $1,353.80