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	$38.73	4.852%	$40.6092	$40.61	$40.60	$40.60
Purchase #2	$46.50	8.737%	$50.5627	$50.56	$50.55	$50.60
Purchase #3	$103.95	7.327%	$111.5664	$111.57	$111.55	$111.60
Purchase #4	$59.41	12.248%	$66.6865	$66.69	$66.70	$66.70
Purchase #5	$108.33	9.613%	$118.7438	$118.74	$118.75	$118.70
Purchase #6	$231.96	11.483%	$258.596	$258.60	$258.60	$258.60
Purchase #7	$245.44	4.743%	$257.0812	$257.08	$257.10	$257.10
7 purchase totals =	$834.32		$903.8458	$903.85	$903.85	$903.90