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 $232.42   13.549%   $263.9106   $263.91   $263.90   $263.90  
  Purchase #2 $60.39   12.533%   $67.9587   $67.96   $67.95   $68.00  
  Purchase #3 $110.28   12.867%   $124.4697   $124.47   $124.45   $124.50  
  Purchase #4 $121.78   12.447%   $136.938   $136.94   $136.95   $136.90  
  Purchase #5 $51.34   8.667%   $55.7896   $55.79   $55.80   $55.80  
  Purchase #6 $221.71   12.604%   $249.6543   $249.65   $249.65   $249.70  
  Purchase #7 $250.97   10.161%   $276.4711   $276.47   $276.45   $276.50  
  7 purchase totals = $1,048.89       $1,175.1920   $1,175.19   $1,175.15   $1,175.30