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	$230.34	3.714%	$238.8948	$238.89	$238.90	$238.90
Purchase #2	$12.81	4.154%	$13.3421	$13.34	$13.35	$13.30
Purchase #3	$225.82	12.209%	$253.3904	$253.39	$253.40	$253.40
Purchase #4	$61.73	7.319%	$66.248	$66.25	$66.25	$66.20
Purchase #5	$212.58	6.166%	$225.6877	$225.69	$225.70	$225.70
Purchase #6	$159.37	3.860%	$165.5217	$165.52	$165.50	$165.50
Purchase #7	$66.87	12.542%	$75.2568	$75.26	$75.25	$75.30
7 purchase totals =	$969.52		$1,038.3415	$1,038.34	$1,038.35	$1,038.30