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	$42.27	11.867%	$47.2862	$47.29	$47.30	$47.30
Purchase #2	$49.36	12.674%	$55.6159	$55.62	$55.60	$55.60
Purchase #3	$165.81	8.313%	$179.5938	$179.59	$179.60	$179.60
Purchase #4	$68.55	12.621%	$77.2017	$77.20	$77.20	$77.20
Purchase #5	$230.86	8.510%	$250.5062	$250.51	$250.50	$250.50
Purchase #6	$104.55	6.774%	$111.6322	$111.63	$111.65	$111.60
Purchase #7	$204.89	12.865%	$231.2491	$231.25	$231.25	$231.20
7 purchase totals =	$866.29		$953.0851	$953.09	$953.10	$953.00