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 $176.46   10.763%   $195.4524   $195.45   $195.45   $195.50  
  Purchase #2 $227.72   5.169%   $239.4908   $239.49   $239.50   $239.50  
  Purchase #3 $52.32   6.103%   $55.5131   $55.51   $55.50   $55.50  
  Purchase #4 $210.36   9.452%   $230.2432   $230.24   $230.25   $230.20  
  Purchase #5 $48.78   7.533%   $52.4546   $52.45   $52.45   $52.50  
  Purchase #6 $52.98   5.678%   $55.9882   $55.99   $56.00   $56.00  
  Purchase #7 $116.29   7.867%   $125.4385   $125.44   $125.45   $125.40  
  7 purchase totals = $884.91       $954.5808   $954.57   $954.60   $954.60