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	$100.74	4.495%	$105.2683	$105.27	$105.25	$105.30
Purchase #2	$237.79	7.197%	$254.9037	$254.90	$254.90	$254.90
Purchase #3	$75.29	8.798%	$81.914	$81.91	$81.90	$81.90
Purchase #4	$123.52	13.111%	$139.7147	$139.71	$139.70	$139.70
Purchase #5	$191.73	11.747%	$214.2525	$214.25	$214.25	$214.30
Purchase #6	$40.25	5.328%	$42.3945	$42.39	$42.40	$42.40
Purchase #7	$146.63	8.147%	$158.5759	$158.58	$158.60	$158.60
7 purchase totals =	$915.95		$997.0236	$997.01	$997.00	$997.10