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	$139.27	3.800%	$144.5623	$144.56	$144.55	$144.60
Purchase #2	$88.32	13.646%	$100.3721	$100.37	$100.35	$100.40
Purchase #3	$204.85	12.519%	$230.4952	$230.50	$230.50	$230.50
Purchase #4	$116.38	6.583%	$124.0413	$124.04	$124.05	$124.00
Purchase #5	$146.84	5.771%	$155.3141	$155.31	$155.30	$155.30
Purchase #6	$93.30	5.280%	$98.2262	$98.23	$98.25	$98.20
Purchase #7	$101.65	6.121%	$107.872	$107.87	$107.85	$107.90
7 purchase totals =	$890.61		$960.8832	$960.88	$960.85	$960.90