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 $231.63   8.278%   $250.8043   $250.80   $250.80   $250.80  
  Purchase #2 $111.47   6.491%   $118.7055   $118.71   $118.70   $118.70  
  Purchase #3 $118.54   9.618%   $129.9412   $129.94   $129.95   $129.90  
  Purchase #4 $162.98   3.523%   $168.7218   $168.72   $168.70   $168.70  
  Purchase #5 $125.36   6.756%   $133.8293   $133.83   $133.85   $133.80  
  Purchase #6 $171.71   3.669%   $178.01   $178.01   $178.00   $178.00  
  Purchase #7 $50.64   9.389%   $55.3946   $55.39   $55.40   $55.40  
  7 purchase totals = $972.33       $1,035.4067   $1,035.40   $1,035.40   $1,035.30