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 $43.49   9.542%   $47.6398   $47.64   $47.65   $47.60  
  Purchase #2 $196.74   13.323%   $222.9517   $222.95   $222.95   $223.00  
  Purchase #3 $117.88   8.272%   $127.631   $127.63   $127.65   $127.60  
  Purchase #4 $225.81   7.120%   $241.8877   $241.89   $241.90   $241.90  
  Purchase #5 $135.75   11.519%   $151.387   $151.39   $151.40   $151.40  
  Purchase #6 $91.77   10.138%   $101.0736   $101.07   $101.05   $101.10  
  Purchase #7 $28.37   8.561%   $30.7988   $30.80   $30.80   $30.80  
  7 purchase totals = $839.81       $923.3696   $923.37   $923.40   $923.40