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 $224.98   12.696%   $253.5435   $253.54   $253.55   $253.50  
  Purchase #2 $204.70   13.716%   $232.7767   $232.78   $232.80   $232.80  
  Purchase #3 $130.86   13.340%   $148.3167   $148.32   $148.30   $148.30  
  Purchase #4 $178.86   3.581%   $185.265   $185.27   $185.25   $185.30  
  Purchase #5 $217.29   12.606%   $244.6816   $244.68   $244.70   $244.70  
  Purchase #6 $182.74   4.521%   $191.0017   $191.00   $191.00   $191.00  
  Purchase #7 $172.45   8.703%   $187.4583   $187.46   $187.45   $187.50  
  7 purchase totals = $1,311.88       $1,443.0435   $1,443.05   $1,443.05   $1,443.10