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 $57.69   13.831%   $65.6691   $65.67   $65.65   $65.70  
  Purchase #2 $207.25   4.322%   $216.2073   $216.21   $216.20   $216.20  
  Purchase #3 $121.68   6.617%   $129.7316   $129.73   $129.75   $129.70  
  Purchase #4 $21.92   7.787%   $23.6269   $23.63   $23.65   $23.60  
  Purchase #5 $11.92   4.111%   $12.41   $12.41   $12.40   $12.40  
  Purchase #6 $148.91   5.790%   $157.5319   $157.53   $157.55   $157.50  
  Purchase #7 $61.97   11.531%   $69.1158   $69.12   $69.10   $69.10  
  7 purchase totals = $631.34       $674.2926   $674.30   $674.30   $674.20