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 $95.63   13.334%   $108.3813   $108.38   $108.40   $108.40  
  Purchase #2 $51.99   7.542%   $55.9111   $55.91   $55.90   $55.90  
  Purchase #3 $175.75   8.256%   $190.2599   $190.26   $190.25   $190.30  
  Purchase #4 $5.39   13.811%   $6.1344   $6.13   $6.15   $6.10  
  Purchase #5 $217.47   13.495%   $246.8176   $246.82   $246.80   $246.80  
  Purchase #6 $136.50   11.339%   $151.9777   $151.98   $152.00   $152.00  
  Purchase #7 $212.41   5.738%   $224.5981   $224.60   $224.60   $224.60  
  7 purchase totals = $895.14       $984.0801   $984.08   $984.10   $984.10