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 $244.78   11.733%   $273.5   $273.50   $273.50   $273.50  
  Purchase #2 $228.77   3.370%   $236.4795   $236.48   $236.50   $236.50  
  Purchase #3 $216.85   11.531%   $241.855   $241.86   $241.85   $241.90  
  Purchase #4 $87.59   8.397%   $94.9449   $94.94   $94.95   $94.90  
  Purchase #5 $233.59   13.523%   $265.1784   $265.18   $265.20   $265.20  
  Purchase #6 $17.40   6.790%   $18.5815   $18.58   $18.60   $18.60  
  Purchase #7 $120.92   13.714%   $137.503   $137.50   $137.50   $137.50  
  7 purchase totals = $1,149.90       $1,268.0423   $1,268.04   $1,268.10   $1,268.10