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	$166.52	3.579%	$172.4798	$172.48	$172.50	$172.50
Purchase #2	$168.66	11.500%	$188.0559	$188.06	$188.05	$188.10
Purchase #3	$69.90	7.452%	$75.1089	$75.11	$75.10	$75.10
Purchase #4	$114.27	11.426%	$127.3265	$127.33	$127.35	$127.30
Purchase #5	$147.88	7.252%	$158.6043	$158.60	$158.60	$158.60
Purchase #6	$66.40	7.784%	$71.5686	$71.57	$71.55	$71.60
Purchase #7	$8.37	4.568%	$8.7523	$8.75	$8.75	$8.80
7 purchase totals =	$742.00		$801.8963	$801.90	$801.90	$802.00