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 $208.64   13.568%   $236.9483   $236.95   $236.95   $236.90  
  Purchase #2 $106.41   4.116%   $110.7898   $110.79   $110.80   $110.80  
  Purchase #3 $207.88   11.714%   $232.2311   $232.23   $232.25   $232.20  
  Purchase #4 $215.85   8.120%   $233.377   $233.38   $233.40   $233.40  
  Purchase #5 $226.76   9.819%   $249.0256   $249.03   $249.05   $249.00  
  Purchase #6 $235.53   6.205%   $250.1446   $250.14   $250.15   $250.10  
  Purchase #7 $25.93   5.240%   $27.2887   $27.29   $27.30   $27.30  
  7 purchase totals = $1,227.00       $1,339.8051   $1,339.81   $1,339.90   $1,339.70