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	$46.42	7.198%	$49.7613	$49.76	$49.75	$49.80
Purchase #2	$236.43	5.412%	$249.2256	$249.23	$249.25	$249.20
Purchase #3	$40.25	11.244%	$44.7757	$44.78	$44.80	$44.80
Purchase #4	$64.92	10.604%	$71.8041	$71.80	$71.80	$71.80
Purchase #5	$150.31	5.627%	$158.7679	$158.77	$158.75	$158.80
Purchase #6	$61.89	7.457%	$66.5051	$66.51	$66.50	$66.50
Purchase #7	$148.64	4.639%	$155.5354	$155.54	$155.55	$155.50
7 purchase totals =	$748.86		$796.3751	$796.39	$796.40	$796.40