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	$10.57	12.181%	$11.8575	$11.86	$11.85	$11.90
Purchase #2	$100.78	4.726%	$105.5429	$105.54	$105.55	$105.50
Purchase #3	$41.61	11.188%	$46.2653	$46.27	$46.25	$46.30
Purchase #4	$52.49	12.441%	$59.0203	$59.02	$59.00	$59.00
Purchase #5	$68.75	11.323%	$76.5346	$76.53	$76.55	$76.50
Purchase #6	$166.81	7.454%	$179.244	$179.24	$179.25	$179.20
Purchase #7	$118.30	13.397%	$134.1487	$134.15	$134.15	$134.10
7 purchase totals =	$559.31		$612.6133	$612.61	$612.60	$612.50