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	$38.45	11.575%	$42.9006	$42.90	$42.90	$42.90
Purchase #2	$250.92	10.770%	$277.9441	$277.94	$277.95	$277.90
Purchase #3	$19.55	13.137%	$22.1183	$22.12	$22.10	$22.10
Purchase #4	$102.51	13.493%	$116.3417	$116.34	$116.35	$116.30
Purchase #5	$211.46	8.123%	$228.6369	$228.64	$228.65	$228.60
Purchase #6	$89.68	12.505%	$100.8945	$100.89	$100.90	$100.90
Purchase #7	$151.90	3.346%	$156.9826	$156.98	$157.00	$157.00
7 purchase totals =	$864.47		$945.8187	$945.81	$945.85	$945.70