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	$165.25	5.820%	$174.8676	$174.87	$174.85	$174.90
Purchase #2	$132.87	13.420%	$150.7012	$150.70	$150.70	$150.70
Purchase #3	$146.72	12.594%	$165.1979	$165.20	$165.20	$165.20
Purchase #4	$91.78	9.404%	$100.411	$100.41	$100.40	$100.40
Purchase #5	$88.40	4.634%	$92.4965	$92.50	$92.50	$92.50
Purchase #6	$213.58	8.316%	$231.3413	$231.34	$231.35	$231.30
Purchase #7	$74.89	9.129%	$81.7267	$81.73	$81.75	$81.70
7 purchase totals =	$913.49		$996.7422	$996.75	$996.75	$996.70