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	$120.45	5.850%	$127.4963	$127.50	$127.50	$127.50
Purchase #2	$35.46	13.282%	$40.1698	$40.17	$40.15	$40.20
Purchase #3	$70.69	13.222%	$80.0366	$80.04	$80.05	$80.00
Purchase #4	$247.98	3.128%	$255.7368	$255.74	$255.75	$255.70
Purchase #5	$113.27	7.593%	$121.8706	$121.87	$121.85	$121.90
Purchase #6	$22.91	11.280%	$25.4942	$25.49	$25.50	$25.50
Purchase #7	$56.33	9.247%	$61.5388	$61.54	$61.55	$61.50
7 purchase totals =	$667.09		$712.3431	$712.35	$712.35	$712.30