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	$74.87	11.627%	$83.5751	$83.58	$83.60	$83.60
Purchase #2	$237.72	13.725%	$270.3471	$270.35	$270.35	$270.30
Purchase #3	$34.77	4.635%	$36.3816	$36.38	$36.40	$36.40
Purchase #4	$127.95	9.209%	$139.7329	$139.73	$139.75	$139.70
Purchase #5	$99.82	5.822%	$105.6315	$105.63	$105.65	$105.60
Purchase #6	$108.32	6.232%	$115.0705	$115.07	$115.05	$115.10
Purchase #7	$44.88	13.139%	$50.7768	$50.78	$50.80	$50.80
7 purchase totals =	$728.33		$801.5155	$801.52	$801.60	$801.50