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	$79.48	12.605%	$89.4985	$89.50	$89.50	$89.50
Purchase #2	$181.33	10.526%	$200.4168	$200.42	$200.40	$200.40
Purchase #3	$239.44	6.562%	$255.1521	$255.15	$255.15	$255.20
Purchase #4	$24.67	8.157%	$26.6823	$26.68	$26.70	$26.70
Purchase #5	$183.56	9.297%	$200.6256	$200.63	$200.65	$200.60
Purchase #6	$146.96	7.805%	$158.4302	$158.43	$158.45	$158.40
Purchase #7	$23.47	7.180%	$25.1551	$25.16	$25.15	$25.20
7 purchase totals =	$878.91		$955.9606	$955.97	$956.00	$956.00