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	$146.61	9.694%	$160.8224	$160.82	$160.80	$160.80
Purchase #2	$189.32	4.668%	$198.1575	$198.16	$198.15	$198.20
Purchase #3	$116.61	11.814%	$130.3863	$130.39	$130.40	$130.40
Purchase #4	$80.99	3.264%	$83.6335	$83.63	$83.65	$83.60
Purchase #5	$162.54	3.446%	$168.1411	$168.14	$168.15	$168.10
Purchase #6	$74.65	5.556%	$78.7976	$78.80	$78.80	$78.80
Purchase #7	$32.82	11.458%	$36.5805	$36.58	$36.60	$36.60
7 purchase totals =	$803.54		$856.5189	$856.52	$856.55	$856.50