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 $53.27   13.548%   $60.487   $60.49   $60.50   $60.50  
  Purchase #2 $200.54   4.147%   $208.8564   $208.86   $208.85   $208.90  
  Purchase #3 $112.94   13.630%   $128.3337   $128.33   $128.35   $128.30  
  Purchase #4 $216.43   9.197%   $236.3351   $236.34   $236.35   $236.30  
  Purchase #5 $12.98   5.222%   $13.6578   $13.66   $13.65   $13.70  
  Purchase #6 $231.53   8.799%   $251.9023   $251.90   $251.90   $251.90  
  Purchase #7 $57.96   11.233%   $64.4706   $64.47   $64.45   $64.50  
  7 purchase totals = $885.65       $964.0429   $964.05   $964.05   $964.10