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	$96.28	6.750%	$102.7789	$102.78	$102.80	$102.80
Purchase #2	$67.50	11.399%	$75.1943	$75.19	$75.20	$75.20
Purchase #3	$192.72	13.122%	$218.0087	$218.01	$218.00	$218.00
Purchase #4	$90.87	10.862%	$100.7403	$100.74	$100.75	$100.70
Purchase #5	$146.68	8.132%	$158.608	$158.61	$158.60	$158.60
Purchase #6	$228.82	4.130%	$238.2703	$238.27	$238.25	$238.30
Purchase #7	$214.48	11.234%	$238.5747	$238.57	$238.55	$238.60
7 purchase totals =	$1,037.35		$1,132.1752	$1,132.17	$1,132.15	$1,132.20