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 $134.56   7.287%   $144.3654   $144.37   $144.35   $144.40  
  Purchase #2 $60.49   10.762%   $66.9999   $67.00   $67.00   $67.00  
  Purchase #3 $84.77   4.733%   $88.7822   $88.78   $88.80   $88.80  
  Purchase #4 $164.79   11.807%   $184.2468   $184.25   $184.25   $184.20  
  Purchase #5 $184.77   3.483%   $191.2055   $191.21   $191.20   $191.20  
  Purchase #6 $176.35   3.312%   $182.1907   $182.19   $182.20   $182.20  
  Purchase #7 $97.92   3.151%   $101.0055   $101.01   $101.00   $101.00  
  7 purchase totals = $903.65       $958.7960   $958.81   $958.80   $958.80