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 $210.89   6.680%   $224.9775   $224.98   $225.00   $225.00  
  Purchase #2 $54.74   7.516%   $58.8543   $58.85   $58.85   $58.90  
  Purchase #3 $91.80   8.595%   $99.6902   $99.69   $99.70   $99.70  
  Purchase #4 $187.73   3.305%   $193.9345   $193.93   $193.95   $193.90  
  Purchase #5 $200.64   10.566%   $221.8396   $221.84   $221.85   $221.80  
  Purchase #6 $146.25   6.113%   $155.1903   $155.19   $155.20   $155.20  
  Purchase #7 $206.53   5.423%   $217.7301   $217.73   $217.75   $217.70  
  7 purchase totals = $1,098.58       $1,172.2165   $1,172.21   $1,172.30   $1,172.20