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 $239.66   6.543%   $255.341   $255.34   $255.35   $255.30  
  Purchase #2 $46.64   5.526%   $49.2173   $49.22   $49.20   $49.20  
  Purchase #3 $120.56   7.673%   $129.8106   $129.81   $129.80   $129.80  
  Purchase #4 $62.26   12.172%   $69.8383   $69.84   $69.85   $69.80  
  Purchase #5 $112.84   6.398%   $120.0595   $120.06   $120.05   $120.10  
  Purchase #6 $125.96   4.528%   $131.6635   $131.66   $131.65   $131.70  
  Purchase #7 $249.54   10.111%   $274.771   $274.77   $274.75   $274.80  
  7 purchase totals = $957.46       $1,030.7012   $1,030.70   $1,030.65   $1,030.70