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 $224.68   12.844%   $253.5379   $253.54   $253.55   $253.50  
  Purchase #2 $62.91   6.611%   $67.069   $67.07   $67.05   $67.10  
  Purchase #3 $49.86   13.200%   $56.4415   $56.44   $56.45   $56.40  
  Purchase #4 $45.29   10.232%   $49.9241   $49.92   $49.90   $49.90  
  Purchase #5 $174.54   10.873%   $193.5177   $193.52   $193.50   $193.50  
  Purchase #6 $173.32   6.814%   $185.13   $185.13   $185.15   $185.10  
  Purchase #7 $170.44   4.853%   $178.7115   $178.71   $178.70   $178.70  
  7 purchase totals = $901.04       $984.3317   $984.33   $984.30   $984.20