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 $215.64   11.170%   $239.727   $239.73   $239.75   $239.70  
  Purchase #2 $40.36   8.429%   $43.7619   $43.76   $43.75   $43.80  
  Purchase #3 $62.88   10.691%   $69.6025   $69.60   $69.60   $69.60  
  Purchase #4 $171.80   7.448%   $184.5957   $184.60   $184.60   $184.60  
  Purchase #5 $165.96   8.866%   $180.674   $180.67   $180.65   $180.70  
  Purchase #6 $214.48   11.628%   $239.4197   $239.42   $239.40   $239.40  
  Purchase #7 $101.77   9.485%   $111.4229   $111.42   $111.40   $111.40  
  7 purchase totals = $972.89       $1,069.2037   $1,069.20   $1,069.15   $1,069.20