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	$90.58	9.465%	$99.1534	$99.15	$99.15	$99.20
Purchase #2	$22.90	5.496%	$24.1586	$24.16	$24.15	$24.20
Purchase #3	$39.88	6.289%	$42.3881	$42.39	$42.40	$42.40
Purchase #4	$144.37	8.643%	$156.8479	$156.85	$156.85	$156.80
Purchase #5	$90.91	8.355%	$98.5055	$98.51	$98.50	$98.50
Purchase #6	$59.82	6.505%	$63.7113	$63.71	$63.70	$63.70
Purchase #7	$220.82	10.624%	$244.2799	$244.28	$244.30	$244.30
7 purchase totals =	$669.28		$729.0447	$729.05	$729.05	$729.10