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	$11.90	7.280%	$12.7663	$12.77	$12.75	$12.80
Purchase #2	$58.45	13.171%	$66.1484	$66.15	$66.15	$66.10
Purchase #3	$249.48	12.776%	$281.3536	$281.35	$281.35	$281.40
Purchase #4	$48.55	5.727%	$51.3305	$51.33	$51.35	$51.30
Purchase #5	$235.77	4.717%	$246.8913	$246.89	$246.90	$246.90
Purchase #6	$186.28	12.116%	$208.8497	$208.85	$208.85	$208.80
Purchase #7	$82.45	10.327%	$90.9646	$90.96	$90.95	$91.00
7 purchase totals =	$872.88		$958.3044	$958.30	$958.30	$958.30