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	$106.76	3.598%	$110.6012	$110.60	$110.60	$110.60
Purchase #2	$132.51	8.536%	$143.8211	$143.82	$143.80	$143.80
Purchase #3	$137.62	5.871%	$145.6997	$145.70	$145.70	$145.70
Purchase #4	$33.82	6.140%	$35.8965	$35.90	$35.90	$35.90
Purchase #5	$29.64	4.799%	$31.0624	$31.06	$31.05	$31.10
Purchase #6	$138.60	3.435%	$143.3609	$143.36	$143.35	$143.40
Purchase #7	$33.47	13.322%	$37.9289	$37.93	$37.95	$37.90
7 purchase totals =	$612.42		$648.3707	$648.37	$648.35	$648.40