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 $33.36   6.629%   $35.5714   $35.57   $35.55   $35.60  
  Purchase #2 $170.88   8.383%   $185.2049   $185.20   $185.20   $185.20  
  Purchase #3 $58.44   3.224%   $60.3241   $60.32   $60.30   $60.30  
  Purchase #4 $250.89   4.584%   $262.3908   $262.39   $262.40   $262.40  
  Purchase #5 $225.83   5.390%   $238.0022   $238.00   $238.00   $238.00  
  Purchase #6 $47.42   12.832%   $53.5049   $53.50   $53.50   $53.50  
  Purchase #7 $160.78   11.178%   $178.752   $178.75   $178.75   $178.80  
  7 purchase totals = $947.60       $1,013.7503   $1,013.73   $1,013.70   $1,013.80