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	$10.53	12.671%	$11.8643	$11.86	$11.85	$11.90
Purchase #2	$204.52	11.345%	$227.7228	$227.72	$227.70	$227.70
Purchase #3	$113.98	12.416%	$128.1318	$128.13	$128.15	$128.10
Purchase #4	$199.40	11.497%	$222.325	$222.33	$222.35	$222.30
Purchase #5	$127.72	4.790%	$133.8378	$133.84	$133.85	$133.80
Purchase #6	$70.72	11.221%	$78.6555	$78.66	$78.65	$78.70
Purchase #7	$44.74	11.654%	$49.954	$49.95	$49.95	$50.00
7 purchase totals =	$771.61		$852.4912	$852.49	$852.50	$852.50