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	$87.72	3.510%	$90.799	$90.80	$90.80	$90.80
Purchase #2	$78.72	7.407%	$84.5508	$84.55	$84.55	$84.60
Purchase #3	$205.64	8.722%	$223.5759	$223.58	$223.60	$223.60
Purchase #4	$134.84	7.707%	$145.2321	$145.23	$145.25	$145.20
Purchase #5	$27.61	3.851%	$28.6733	$28.67	$28.65	$28.70
Purchase #6	$132.50	5.854%	$140.2566	$140.26	$140.25	$140.30
Purchase #7	$182.61	7.556%	$196.408	$196.41	$196.40	$196.40
7 purchase totals =	$849.64		$909.4957	$909.50	$909.50	$909.60