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	$96.52	3.586%	$99.9812	$99.98	$100.00	$100.00
Purchase #2	$247.54	7.378%	$265.8035	$265.80	$265.80	$265.80
Purchase #3	$52.26	12.788%	$58.943	$58.94	$58.95	$58.90
Purchase #4	$147.98	13.427%	$167.8493	$167.85	$167.85	$167.80
Purchase #5	$190.94	13.598%	$216.904	$216.90	$216.90	$216.90
Purchase #6	$6.70	12.478%	$7.536	$7.54	$7.55	$7.50
Purchase #7	$99.33	12.359%	$111.6062	$111.61	$111.60	$111.60
7 purchase totals =	$841.27		$928.6232	$928.62	$928.65	$928.50