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	$34.42	13.436%	$39.0447	$39.04	$39.05	$39.00
Purchase #2	$234.31	10.473%	$258.8493	$258.85	$258.85	$258.80
Purchase #3	$105.36	13.795%	$119.8944	$119.89	$119.90	$119.90
Purchase #4	$146.27	10.764%	$162.0145	$162.01	$162.00	$162.00
Purchase #5	$147.53	7.377%	$158.4133	$158.41	$158.40	$158.40
Purchase #6	$93.37	8.240%	$101.0637	$101.06	$101.05	$101.10
Purchase #7	$238.98	6.563%	$254.6643	$254.66	$254.65	$254.70
7 purchase totals =	$1,000.24		$1,093.9442	$1,093.92	$1,093.90	$1,093.90