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 $214.86   10.642%   $237.7254   $237.73   $237.75   $237.70  
  Purchase #2 $122.91   8.732%   $133.6425   $133.64   $133.65   $133.60  
  Purchase #3 $17.48   11.616%   $19.5105   $19.51   $19.50   $19.50  
  Purchase #4 $168.73   11.761%   $188.5743   $188.57   $188.55   $188.60  
  Purchase #5 $121.87   12.364%   $136.938   $136.94   $136.95   $136.90  
  Purchase #6 $199.72   8.129%   $215.9552   $215.96   $215.95   $216.00  
  Purchase #7 $33.98   5.295%   $35.7792   $35.78   $35.80   $35.80  
  7 purchase totals = $879.55       $968.1251   $968.13   $968.15   $968.10