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	$170.30	11.543%	$189.9577	$189.96	$189.95	$190.00
Purchase #2	$243.90	5.188%	$256.5535	$256.55	$256.55	$256.60
Purchase #3	$131.33	13.326%	$148.831	$148.83	$148.85	$148.80
Purchase #4	$114.82	4.712%	$120.2303	$120.23	$120.25	$120.20
Purchase #5	$10.30	5.116%	$10.8269	$10.83	$10.85	$10.80
Purchase #6	$28.89	12.539%	$32.5125	$32.51	$32.50	$32.50
Purchase #7	$145.70	8.127%	$157.541	$157.54	$157.55	$157.50
7 purchase totals =	$845.24		$916.4529	$916.45	$916.50	$916.40