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 $241.44   13.374%   $273.7302   $273.73   $273.75   $273.70  
  Purchase #2 $23.49   12.610%   $26.4521   $26.45   $26.45   $26.50  
  Purchase #3 $207.28   10.859%   $229.7885   $229.79   $229.80   $229.80  
  Purchase #4 $151.49   4.384%   $158.1313   $158.13   $158.15   $158.10  
  Purchase #5 $101.33   13.753%   $115.2659   $115.27   $115.25   $115.30  
  Purchase #6 $238.75   6.161%   $253.4594   $253.46   $253.45   $253.50  
  Purchase #7 $166.84   10.556%   $184.4516   $184.45   $184.45   $184.50  
  7 purchase totals = $1,130.62       $1,241.2790   $1,241.28   $1,241.30   $1,241.40