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 $228.60   12.559%   $257.3099   $257.31   $257.30   $257.30  
  Purchase #2 $84.93   13.356%   $96.2733   $96.27   $96.25   $96.30  
  Purchase #3 $194.41   5.599%   $205.295   $205.30   $205.30   $205.30  
  Purchase #4 $76.76   12.596%   $86.4287   $86.43   $86.45   $86.40  
  Purchase #5 $63.63   4.191%   $66.2967   $66.30   $66.30   $66.30  
  Purchase #6 $137.94   11.431%   $153.7079   $153.71   $153.70   $153.70  
  Purchase #7 $246.76   13.820%   $280.8622   $280.86   $280.85   $280.90  
  7 purchase totals = $1,033.03       $1,146.1737   $1,146.18   $1,146.15   $1,146.20