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 $65.33   4.281%   $68.1268   $68.13   $68.15   $68.10  
  Purchase #2 $178.73   4.313%   $186.4386   $186.44   $186.45   $186.40  
  Purchase #3 $127.97   4.421%   $133.6276   $133.63   $133.65   $133.60  
  Purchase #4 $93.77   11.656%   $104.6998   $104.70   $104.70   $104.70  
  Purchase #5 $73.39   5.382%   $77.3398   $77.34   $77.35   $77.30  
  Purchase #6 $161.48   5.591%   $170.5083   $170.51   $170.50   $170.50  
  Purchase #7 $21.29   6.417%   $22.6562   $22.66   $22.65   $22.70  
  7 purchase totals = $721.96       $763.3971   $763.41   $763.45   $763.30