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	$62.72	5.386%	$66.0981	$66.10	$66.10	$66.10
Purchase #2	$218.28	12.177%	$244.86	$244.86	$244.85	$244.90
Purchase #3	$159.46	5.613%	$168.4105	$168.41	$168.40	$168.40
Purchase #4	$8.90	8.815%	$9.6845	$9.68	$9.70	$9.70
Purchase #5	$36.63	12.658%	$41.2666	$41.27	$41.25	$41.30
Purchase #6	$250.73	9.868%	$275.472	$275.47	$275.45	$275.50
Purchase #7	$64.29	13.433%	$72.9261	$72.93	$72.95	$72.90
7 purchase totals =	$801.01		$878.7178	$878.72	$878.70	$878.80