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 $218.79   10.582%   $241.9424   $241.94   $241.95   $241.90  
  Purchase #2 $227.89   5.143%   $239.6104   $239.61   $239.60   $239.60  
  Purchase #3 $72.79   13.265%   $82.4456   $82.45   $82.45   $82.40  
  Purchase #4 $154.29   3.377%   $159.5004   $159.50   $159.50   $159.50  
  Purchase #5 $13.92   4.335%   $14.5234   $14.52   $14.50   $14.50  
  Purchase #6 $75.57   11.748%   $84.448   $84.45   $84.45   $84.40  
  Purchase #7 $5.88   6.574%   $6.2666   $6.27   $6.25   $6.30  
  7 purchase totals = $769.13       $828.7368   $828.74   $828.70   $828.60