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	$144.80	11.374%	$161.2696	$161.27	$161.25	$161.30
Purchase #2	$88.37	12.488%	$99.4056	$99.41	$99.40	$99.40
Purchase #3	$45.97	11.429%	$51.2239	$51.22	$51.20	$51.20
Purchase #4	$57.55	4.166%	$59.9475	$59.95	$59.95	$59.90
Purchase #5	$160.46	9.445%	$175.6154	$175.62	$175.60	$175.60
Purchase #6	$152.35	13.658%	$173.158	$173.16	$173.15	$173.20
Purchase #7	$100.42	7.117%	$107.5669	$107.57	$107.55	$107.60
7 purchase totals =	$749.92		$828.1869	$828.20	$828.10	$828.20