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	$133.51	12.169%	$149.7568	$149.76	$149.75	$149.80
Purchase #2	$65.84	10.326%	$72.6386	$72.64	$72.65	$72.60
Purchase #3	$34.52	13.276%	$39.1029	$39.10	$39.10	$39.10
Purchase #4	$224.38	8.131%	$242.6243	$242.62	$242.60	$242.60
Purchase #5	$86.54	13.789%	$98.473	$98.47	$98.45	$98.50
Purchase #6	$234.47	4.446%	$244.8945	$244.89	$244.90	$244.90
Purchase #7	$183.28	8.789%	$199.3885	$199.39	$199.40	$199.40
7 purchase totals =	$962.54		$1,046.8786	$1,046.87	$1,046.85	$1,046.90