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 $217.56   12.218%   $244.1415   $244.14   $244.15   $244.10  
  Purchase #2 $154.64   12.363%   $173.7581   $173.76   $173.75   $173.80  
  Purchase #3 $76.25   8.422%   $82.6718   $82.67   $82.65   $82.70  
  Purchase #4 $143.93   11.370%   $160.2948   $160.29   $160.30   $160.30  
  Purchase #5 $217.51   3.211%   $224.4942   $224.49   $224.50   $224.50  
  Purchase #6 $143.42   13.859%   $163.2966   $163.30   $163.30   $163.30  
  Purchase #7 $71.98   5.466%   $75.9144   $75.91   $75.90   $75.90  
  7 purchase totals = $1,025.29       $1,124.5714   $1,124.56   $1,124.55   $1,124.60