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 $60.49   10.289%   $66.7138   $66.71   $66.70   $66.70  
  Purchase #2 $71.29   3.453%   $73.7516   $73.75   $73.75   $73.80  
  Purchase #3 $60.28   5.239%   $63.4381   $63.44   $63.45   $63.40  
  Purchase #4 $60.92   11.516%   $67.9355   $67.94   $67.95   $67.90  
  Purchase #5 $25.48   11.864%   $28.5029   $28.50   $28.50   $28.50  
  Purchase #6 $208.56   13.114%   $235.9106   $235.91   $235.90   $235.90  
  Purchase #7 $72.36   3.255%   $74.7153   $74.72   $74.70   $74.70  
  7 purchase totals = $559.38       $610.9678   $610.97   $610.95   $610.90