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	$237.46	7.201%	$254.5595	$254.56	$254.55	$254.60
Purchase #2	$228.81	11.649%	$255.4641	$255.46	$255.45	$255.50
Purchase #3	$92.40	7.222%	$99.0731	$99.07	$99.05	$99.10
Purchase #4	$37.50	10.868%	$41.5755	$41.58	$41.60	$41.60
Purchase #5	$9.71	11.760%	$10.8519	$10.85	$10.85	$10.90
Purchase #6	$42.87	9.382%	$46.8921	$46.89	$46.90	$46.90
Purchase #7	$97.69	5.389%	$102.9545	$102.95	$102.95	$103.00
7 purchase totals =	$746.44		$811.3707	$811.36	$811.35	$811.60