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	$172.44	9.325%	$188.52	$188.52	$188.50	$188.50
Purchase #2	$151.64	10.339%	$167.3181	$167.32	$167.30	$167.30
Purchase #3	$155.50	13.611%	$176.6651	$176.67	$176.65	$176.70
Purchase #4	$153.77	6.831%	$164.274	$164.27	$164.25	$164.30
Purchase #5	$37.36	9.526%	$40.9189	$40.92	$40.90	$40.90
Purchase #6	$143.25	12.410%	$161.0273	$161.03	$161.05	$161.00
Purchase #7	$231.40	5.619%	$244.4024	$244.40	$244.40	$244.40
7 purchase totals =	$1,045.36		$1,143.1258	$1,143.13	$1,143.05	$1,143.10