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	$242.98	13.428%	$275.6074	$275.61	$275.60	$275.60
Purchase #2	$15.97	10.559%	$17.6563	$17.66	$17.65	$17.70
Purchase #3	$113.51	12.301%	$127.4729	$127.47	$127.45	$127.50
Purchase #4	$138.91	8.152%	$150.2339	$150.23	$150.25	$150.20
Purchase #5	$234.86	12.543%	$264.3185	$264.32	$264.30	$264.30
Purchase #6	$73.37	6.507%	$78.1442	$78.14	$78.15	$78.10
Purchase #7	$203.61	13.333%	$230.7573	$230.76	$230.75	$230.80
7 purchase totals =	$1,023.21		$1,144.1905	$1,144.19	$1,144.15	$1,144.20