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 $48.67   7.733%   $52.4337   $52.43   $52.45   $52.40  
  Purchase #2 $119.98   4.712%   $125.6335   $125.63   $125.65   $125.60  
  Purchase #3 $13.77   10.257%   $15.1824   $15.18   $15.20   $15.20  
  Purchase #4 $124.53   7.179%   $133.47   $133.47   $133.45   $133.50  
  Purchase #5 $67.69   5.222%   $71.2248   $71.22   $71.20   $71.20  
  Purchase #6 $196.96   3.574%   $203.9994   $204.00   $204.00   $204.00  
  Purchase #7 $238.62   9.848%   $262.1193   $262.12   $262.10   $262.10  
  7 purchase totals = $810.22       $864.0631   $864.05   $864.05   $864.00