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	$244.53	13.710%	$278.0551	$278.06	$278.05	$278.10
Purchase #2	$130.31	12.482%	$146.5753	$146.58	$146.60	$146.60
Purchase #3	$15.26	9.429%	$16.6989	$16.70	$16.70	$16.70
Purchase #4	$7.79	9.751%	$8.5496	$8.55	$8.55	$8.50
Purchase #5	$90.70	11.263%	$100.9155	$100.92	$100.90	$100.90
Purchase #6	$160.50	4.567%	$167.83	$167.83	$167.85	$167.80
Purchase #7	$177.37	10.716%	$196.377	$196.38	$196.40	$196.40
7 purchase totals =	$826.46		$915.0014	$915.02	$915.05	$915.00