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 $64.94   7.772%   $69.9871   $69.99   $70.00   $70.00  
  Purchase #2 $22.71   12.601%   $25.5717   $25.57   $25.55   $25.60  
  Purchase #3 $227.77   5.837%   $241.0649   $241.06   $241.05   $241.10  
  Purchase #4 $224.63   3.855%   $233.2895   $233.29   $233.30   $233.30  
  Purchase #5 $127.25   4.245%   $132.6518   $132.65   $132.65   $132.70  
  Purchase #6 $170.93   6.655%   $182.3054   $182.31   $182.30   $182.30  
  Purchase #7 $64.67   10.200%   $71.2663   $71.27   $71.25   $71.30  
  7 purchase totals = $902.90       $956.1367   $956.14   $956.10   $956.30