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	$32.39	9.636%	$35.5111	$35.51	$35.50	$35.50
Purchase #2	$39.62	3.203%	$40.889	$40.89	$40.90	$40.90
Purchase #3	$115.89	10.154%	$127.6575	$127.66	$127.65	$127.70
Purchase #4	$149.60	10.335%	$165.0612	$165.06	$165.05	$165.10
Purchase #5	$85.28	10.845%	$94.5286	$94.53	$94.55	$94.50
Purchase #6	$228.39	12.125%	$256.0823	$256.08	$256.10	$256.10
Purchase #7	$77.94	13.400%	$88.384	$88.38	$88.40	$88.40
7 purchase totals =	$729.11		$808.1137	$808.11	$808.15	$808.20