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 $50.28   12.426%   $56.5278   $56.53   $56.55   $56.50  
  Purchase #2 $210.45   13.733%   $239.3511   $239.35   $239.35   $239.40  
  Purchase #3 $46.87   13.130%   $53.024   $53.02   $53.00   $53.00  
  Purchase #4 $33.53   7.857%   $36.1645   $36.16   $36.15   $36.20  
  Purchase #5 $236.66   12.660%   $266.6212   $266.62   $266.60   $266.60  
  Purchase #6 $231.39   13.355%   $262.2921   $262.29   $262.30   $262.30  
  Purchase #7 $230.59   3.560%   $238.799   $238.80   $238.80   $238.80  
  7 purchase totals = $1,039.77       $1,152.7797   $1,152.77   $1,152.75   $1,152.80