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	$44.81	13.185%	$50.7182	$50.72	$50.70	$50.70
Purchase #2	$93.43	4.154%	$97.3111	$97.31	$97.30	$97.30
Purchase #3	$20.40	5.151%	$21.4508	$21.45	$21.45	$21.50
Purchase #4	$236.53	6.483%	$251.8642	$251.86	$251.85	$251.90
Purchase #5	$187.55	11.688%	$209.4708	$209.47	$209.45	$209.50
Purchase #6	$135.94	11.707%	$151.8545	$151.85	$151.85	$151.90
Purchase #7	$119.40	3.340%	$123.388	$123.39	$123.40	$123.40
7 purchase totals =	$838.06		$906.0576	$906.05	$906.00	$906.20