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 $228.67   13.600%   $259.7691   $259.77   $259.75   $259.80  
  Purchase #2 $46.69   11.382%   $52.0043   $52.00   $52.00   $52.00  
  Purchase #3 $208.96   13.362%   $236.8812   $236.88   $236.90   $236.90  
  Purchase #4 $86.30   13.184%   $97.6778   $97.68   $97.70   $97.70  
  Purchase #5 $241.83   5.341%   $254.7461   $254.75   $254.75   $254.70  
  Purchase #6 $98.92   7.635%   $106.4725   $106.47   $106.45   $106.50  
  Purchase #7 $227.38   9.567%   $249.1334   $249.13   $249.15   $249.10  
  7 purchase totals = $1,138.75       $1,256.6844   $1,256.68   $1,256.70   $1,256.70