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 $212.46   5.733%   $224.6403   $224.64   $224.65   $224.60  
  Purchase #2 $11.47   11.646%   $12.8058   $12.81   $12.80   $12.80  
  Purchase #3 $20.26   11.205%   $22.5301   $22.53   $22.55   $22.50  
  Purchase #4 $200.83   10.847%   $222.614   $222.61   $222.60   $222.60  
  Purchase #5 $242.65   8.838%   $264.0954   $264.10   $264.10   $264.10  
  Purchase #6 $64.39   8.690%   $69.9855   $69.99   $70.00   $70.00  
  Purchase #7 $14.42   4.160%   $15.0199   $15.02   $15.00   $15.00  
  7 purchase totals = $766.48       $831.6910   $831.70   $831.70   $831.60