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 $225.38   12.351%   $253.2167   $253.22   $253.20   $253.20  
  Purchase #2 $175.52   9.605%   $192.3787   $192.38   $192.40   $192.40  
  Purchase #3 $82.83   11.347%   $92.2287   $92.23   $92.25   $92.20  
  Purchase #4 $141.87   3.310%   $146.5659   $146.57   $146.55   $146.60  
  Purchase #5 $119.97   12.755%   $135.2722   $135.27   $135.25   $135.30  
  Purchase #6 $153.98   4.782%   $161.3433   $161.34   $161.35   $161.30  
  Purchase #7 $207.95   9.308%   $227.306   $227.31   $227.30   $227.30  
  7 purchase totals = $1,107.50       $1,208.3115   $1,208.32   $1,208.30   $1,208.30