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	$209.76	12.136%	$235.2165	$235.22	$235.20	$235.20
Purchase #2	$165.41	4.780%	$173.3166	$173.32	$173.30	$173.30
Purchase #3	$19.64	6.256%	$20.8687	$20.87	$20.85	$20.90
Purchase #4	$35.72	3.608%	$37.0088	$37.01	$37.00	$37.00
Purchase #5	$97.94	13.222%	$110.8896	$110.89	$110.90	$110.90
Purchase #6	$47.93	4.148%	$49.9181	$49.92	$49.90	$49.90
Purchase #7	$145.72	3.668%	$151.065	$151.07	$151.05	$151.10
7 purchase totals =	$722.12		$778.2833	$778.30	$778.20	$778.30