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	$112.25	9.240%	$122.6219	$122.62	$122.60	$122.60
Purchase #2	$89.83	11.370%	$100.0437	$100.04	$100.05	$100.00
Purchase #3	$138.41	9.489%	$151.5437	$151.54	$151.55	$151.50
Purchase #4	$152.32	13.411%	$172.7476	$172.75	$172.75	$172.70
Purchase #5	$193.47	8.612%	$210.1316	$210.13	$210.15	$210.10
Purchase #6	$201.97	13.716%	$229.6722	$229.67	$229.65	$229.70
Purchase #7	$152.96	10.780%	$169.4491	$169.45	$169.45	$169.40
7 purchase totals =	$1,041.21		$1,156.2098	$1,156.20	$1,156.20	$1,156.00