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	$68.57	7.196%	$73.5043	$73.50	$73.50	$73.50
Purchase #2	$49.33	5.831%	$52.2064	$52.21	$52.20	$52.20
Purchase #3	$11.37	10.830%	$12.6014	$12.60	$12.60	$12.60
Purchase #4	$120.82	12.798%	$136.2825	$136.28	$136.30	$136.30
Purchase #5	$32.32	10.823%	$35.818	$35.82	$35.80	$35.80
Purchase #6	$47.28	13.843%	$53.825	$53.83	$53.85	$53.80
Purchase #7	$183.53	3.405%	$189.7792	$189.78	$189.80	$189.80
7 purchase totals =	$513.22		$554.0168	$554.02	$554.05	$554.00