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	$250.66	9.205%	$273.7333	$273.73	$273.75	$273.70
Purchase #2	$156.60	9.485%	$171.4535	$171.45	$171.45	$171.50
Purchase #3	$152.79	12.840%	$172.4082	$172.41	$172.40	$172.40
Purchase #4	$100.74	13.558%	$114.3983	$114.40	$114.40	$114.40
Purchase #5	$42.69	8.370%	$46.2632	$46.26	$46.25	$46.30
Purchase #6	$122.59	4.120%	$127.6407	$127.64	$127.65	$127.60
Purchase #7	$240.66	4.389%	$251.2226	$251.22	$251.20	$251.20
7 purchase totals =	$1,066.73		$1,157.1198	$1,157.11	$1,157.10	$1,157.10