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 $104.40   13.118%   $118.0952   $118.10   $118.10   $118.10  
  Purchase #2 $91.92   10.695%   $101.7508   $101.75   $101.75   $101.80  
  Purchase #3 $67.42   11.664%   $75.2839   $75.28   $75.30   $75.30  
  Purchase #4 $176.89   6.621%   $188.6019   $188.60   $188.60   $188.60  
  Purchase #5 $25.84   3.248%   $26.6793   $26.68   $26.70   $26.70  
  Purchase #6 $33.26   3.445%   $34.4058   $34.41   $34.40   $34.40  
  Purchase #7 $175.27   9.538%   $191.9873   $191.99   $192.00   $192.00  
  7 purchase totals = $675.00       $736.8042   $736.81   $736.85   $736.90