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	$204.62	13.245%	$231.7219	$231.72	$231.70	$231.70
Purchase #2	$146.32	13.811%	$166.5283	$166.53	$166.55	$166.50
Purchase #3	$126.72	8.745%	$137.8017	$137.80	$137.80	$137.80
Purchase #4	$191.34	4.613%	$200.1665	$200.17	$200.15	$200.20
Purchase #5	$49.94	11.169%	$55.5178	$55.52	$55.50	$55.50
Purchase #6	$36.63	5.401%	$38.6084	$38.61	$38.60	$38.60
Purchase #7	$137.41	3.112%	$141.6862	$141.69	$141.70	$141.70
7 purchase totals =	$892.98		$972.0308	$972.04	$972.00	$972.00