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	$134.32	12.642%	$151.3007	$151.30	$151.30	$151.30
Purchase #2	$157.86	10.366%	$174.2238	$174.22	$174.20	$174.20
Purchase #3	$47.49	11.608%	$53.0026	$53.00	$53.00	$53.00
Purchase #4	$23.94	5.191%	$25.1827	$25.18	$25.20	$25.20
Purchase #5	$128.95	12.714%	$145.3447	$145.34	$145.35	$145.30
Purchase #6	$38.89	5.191%	$40.9088	$40.91	$40.90	$40.90
Purchase #7	$108.85	4.838%	$114.1162	$114.12	$114.10	$114.10
7 purchase totals =	$640.30		$704.0795	$704.07	$704.05	$704.00