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 $61.59   6.170%   $65.3901   $65.39   $65.40   $65.40  
  Purchase #2 $226.81   7.306%   $243.3807   $243.38   $243.40   $243.40  
  Purchase #3 $30.79   11.735%   $34.4032   $34.40   $34.40   $34.40  
  Purchase #4 $195.82   5.667%   $206.9171   $206.92   $206.90   $206.90  
  Purchase #5 $249.76   5.548%   $263.6167   $263.62   $263.60   $263.60  
  Purchase #6 $184.55   11.410%   $205.6072   $205.61   $205.60   $205.60  
  Purchase #7 $219.71   7.800%   $236.8474   $236.85   $236.85   $236.80  
  7 purchase totals = $1,169.03       $1,256.1624   $1,256.17   $1,256.15   $1,256.10