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	$44.53	5.285%	$46.8834	$46.88	$46.90	$46.90
Purchase #2	$231.97	10.700%	$256.7908	$256.79	$256.80	$256.80
Purchase #3	$33.28	13.564%	$37.7941	$37.79	$37.80	$37.80
Purchase #4	$17.85	7.150%	$19.1263	$19.13	$19.15	$19.10
Purchase #5	$244.82	13.407%	$277.643	$277.64	$277.65	$277.60
Purchase #6	$80.37	4.352%	$83.8677	$83.87	$83.85	$83.90
Purchase #7	$17.47	7.479%	$18.7766	$18.78	$18.80	$18.80
7 purchase totals =	$670.29		$740.8819	$740.88	$740.95	$740.90