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	$58.49	10.355%	$64.5466	$64.55	$64.55	$64.50
Purchase #2	$82.89	10.120%	$91.2785	$91.28	$91.30	$91.30
Purchase #3	$93.65	6.600%	$99.8309	$99.83	$99.85	$99.80
Purchase #4	$154.43	12.422%	$173.6133	$173.61	$173.60	$173.60
Purchase #5	$115.59	10.180%	$127.3571	$127.36	$127.35	$127.40
Purchase #6	$94.68	8.445%	$102.6757	$102.68	$102.70	$102.70
Purchase #7	$121.42	7.520%	$130.5508	$130.55	$130.55	$130.60
7 purchase totals =	$721.15		$789.8529	$789.86	$789.90	$789.90