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 $32.67   4.771%   $34.2287   $34.23   $34.25   $34.20  
  Purchase #2 $125.92   5.118%   $132.3646   $132.36   $132.35   $132.40  
  Purchase #3 $59.61   7.277%   $63.9478   $63.95   $63.95   $63.90  
  Purchase #4 $227.31   11.555%   $253.5757   $253.58   $253.60   $253.60  
  Purchase #5 $111.67   3.644%   $115.7393   $115.74   $115.75   $115.70  
  Purchase #6 $141.42   3.587%   $146.4927   $146.49   $146.50   $146.50  
  Purchase #7 $65.38   13.540%   $74.2325   $74.23   $74.25   $74.20  
  7 purchase totals = $763.98       $820.5813   $820.58   $820.65   $820.50