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	$126.90	13.637%	$144.2054	$144.21	$144.20	$144.20
Purchase #2	$37.71	6.584%	$40.1928	$40.19	$40.20	$40.20
Purchase #3	$48.87	3.795%	$50.7246	$50.72	$50.70	$50.70
Purchase #4	$171.89	13.495%	$195.0866	$195.09	$195.10	$195.10
Purchase #5	$66.62	12.323%	$74.8296	$74.83	$74.85	$74.80
Purchase #6	$99.92	12.534%	$112.444	$112.44	$112.45	$112.40
Purchase #7	$110.63	11.397%	$123.2385	$123.24	$123.25	$123.20
7 purchase totals =	$662.54		$740.7215	$740.72	$740.75	$740.60