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	$124.31	13.828%	$141.4996	$141.50	$141.50	$141.50
Purchase #2	$129.61	5.816%	$137.1481	$137.15	$137.15	$137.10
Purchase #3	$163.38	6.263%	$173.6125	$173.61	$173.60	$173.60
Purchase #4	$18.77	12.528%	$21.1215	$21.12	$21.10	$21.10
Purchase #5	$69.65	13.179%	$78.8292	$78.83	$78.85	$78.80
Purchase #6	$64.93	3.734%	$67.3545	$67.35	$67.35	$67.40
Purchase #7	$197.37	8.793%	$214.7247	$214.72	$214.70	$214.70
7 purchase totals =	$768.02		$834.2901	$834.28	$834.25	$834.20