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	$172.82	11.693%	$193.0278	$193.03	$193.05	$193.00
Purchase #2	$235.66	5.200%	$247.9143	$247.91	$247.90	$247.90
Purchase #3	$70.61	10.824%	$78.2528	$78.25	$78.25	$78.30
Purchase #4	$104.79	3.377%	$108.3288	$108.33	$108.35	$108.30
Purchase #5	$166.36	4.564%	$173.9527	$173.95	$173.95	$174.00
Purchase #6	$75.93	12.353%	$85.3096	$85.31	$85.30	$85.30
Purchase #7	$167.42	10.581%	$185.1347	$185.13	$185.15	$185.10
7 purchase totals =	$993.59		$1,071.9207	$1,071.91	$1,071.95	$1,071.90