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 $241.68   3.431%   $249.972   $249.97   $249.95   $250.00  
  Purchase #2 $42.64   4.682%   $44.6364   $44.64   $44.65   $44.60  
  Purchase #3 $165.40   9.804%   $181.6158   $181.62   $181.60   $181.60  
  Purchase #4 $238.79   9.674%   $261.8905   $261.89   $261.90   $261.90  
  Purchase #5 $86.26   11.750%   $96.3956   $96.40   $96.40   $96.40  
  Purchase #6 $171.90   4.575%   $179.7644   $179.76   $179.75   $179.80  
  Purchase #7 $25.46   8.642%   $27.6603   $27.66   $27.65   $27.70  
  7 purchase totals = $972.13       $1,041.9350   $1,041.94   $1,041.90   $1,042.00