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	$240.78	5.103%	$253.067	$253.07	$253.05	$253.10
Purchase #2	$159.98	13.383%	$181.3901	$181.39	$181.40	$181.40
Purchase #3	$50.99	10.211%	$56.1966	$56.20	$56.20	$56.20
Purchase #4	$96.51	13.255%	$109.3024	$109.30	$109.30	$109.30
Purchase #5	$16.86	10.263%	$18.5903	$18.59	$18.60	$18.60
Purchase #6	$240.60	12.777%	$271.3415	$271.34	$271.35	$271.30
Purchase #7	$18.94	13.423%	$21.4823	$21.48	$21.50	$21.50
7 purchase totals =	$824.66		$911.3702	$911.37	$911.40	$911.40