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 $24.77   6.183%   $26.3015   $26.30   $26.30   $26.30  
  Purchase #2 $125.79   7.482%   $135.2016   $135.20   $135.20   $135.20  
  Purchase #3 $230.92   8.843%   $251.3403   $251.34   $251.35   $251.30  
  Purchase #4 $208.38   5.437%   $219.7096   $219.71   $219.70   $219.70  
  Purchase #5 $226.33   10.295%   $249.6307   $249.63   $249.65   $249.60  
  Purchase #6 $112.43   5.733%   $118.8756   $118.88   $118.90   $118.90  
  Purchase #7 $125.38   5.150%   $131.8371   $131.84   $131.85   $131.80  
  7 purchase totals = $1,054.00       $1,132.8964   $1,132.90   $1,132.95   $1,132.80