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 $51.27   8.748%   $55.7551   $55.76   $55.75   $55.80  
  Purchase #2 $198.41   13.266%   $224.7311   $224.73   $224.75   $224.70  
  Purchase #3 $7.95   13.723%   $9.041   $9.04   $9.05   $9.00  
  Purchase #4 $244.43   10.204%   $269.3716   $269.37   $269.35   $269.40  
  Purchase #5 $153.56   5.334%   $161.7509   $161.75   $161.75   $161.80  
  Purchase #6 $226.61   10.169%   $249.654   $249.65   $249.65   $249.70  
  Purchase #7 $5.35   7.566%   $5.7548   $5.75   $5.75   $5.80  
  7 purchase totals = $887.58       $976.0585   $976.05   $976.05   $976.20