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	$181.52	10.400%	$200.3981	$200.40	$200.40	$200.40
Purchase #2	$182.48	4.456%	$190.6113	$190.61	$190.60	$190.60
Purchase #3	$249.89	6.327%	$265.7005	$265.70	$265.70	$265.70
Purchase #4	$64.91	8.845%	$70.6513	$70.65	$70.65	$70.70
Purchase #5	$155.47	10.849%	$172.3369	$172.34	$172.35	$172.30
Purchase #6	$235.76	11.871%	$263.7471	$263.75	$263.75	$263.70
Purchase #7	$108.37	7.263%	$116.2409	$116.24	$116.25	$116.20
7 purchase totals =	$1,178.40		$1,279.6861	$1,279.69	$1,279.70	$1,279.60