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	$85.65	6.155%	$90.9218	$90.92	$90.90	$90.90
Purchase #2	$250.67	12.442%	$281.8584	$281.86	$281.85	$281.90
Purchase #3	$128.58	3.642%	$133.2629	$133.26	$133.25	$133.30
Purchase #4	$35.77	10.290%	$39.4507	$39.45	$39.45	$39.50
Purchase #5	$173.28	3.636%	$179.5805	$179.58	$179.60	$179.60
Purchase #6	$230.55	5.651%	$243.5784	$243.58	$243.60	$243.60
Purchase #7	$172.64	8.353%	$187.0606	$187.06	$187.05	$187.10
7 purchase totals =	$1,077.14		$1,155.7133	$1,155.71	$1,155.70	$1,155.90