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 $53.91   13.600%   $61.2418   $61.24   $61.25   $61.20  
  Purchase #2 $95.98   9.119%   $104.7324   $104.73   $104.75   $104.70  
  Purchase #3 $59.83   7.167%   $64.118   $64.12   $64.10   $64.10  
  Purchase #4 $68.53   13.275%   $77.6274   $77.63   $77.65   $77.60  
  Purchase #5 $106.80   12.336%   $119.9748   $119.97   $119.95   $120.00  
  Purchase #6 $229.92   11.125%   $255.4986   $255.50   $255.50   $255.50  
  Purchase #7 $63.57   8.327%   $68.8635   $68.86   $68.85   $68.90  
  7 purchase totals = $678.54       $752.0565   $752.05   $752.05   $752.00