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	$79.92	13.428%	$90.6517	$90.65	$90.65	$90.70
Purchase #2	$134.94	5.815%	$142.7868	$142.79	$142.80	$142.80
Purchase #3	$238.57	7.238%	$255.8377	$255.84	$255.85	$255.80
Purchase #4	$74.95	6.181%	$79.5827	$79.58	$79.60	$79.60
Purchase #5	$129.76	3.723%	$134.591	$134.59	$134.60	$134.60
Purchase #6	$50.87	13.481%	$57.7278	$57.73	$57.75	$57.70
Purchase #7	$20.31	12.174%	$22.7825	$22.78	$22.80	$22.80
7 purchase totals =	$729.32		$783.9602	$783.96	$784.05	$784.00