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	$11.39	13.844%	$12.9668	$12.97	$12.95	$13.00
Purchase #2	$40.79	12.520%	$45.8969	$45.90	$45.90	$45.90
Purchase #3	$49.41	10.158%	$54.4291	$54.43	$54.45	$54.40
Purchase #4	$154.85	10.530%	$171.1557	$171.16	$171.15	$171.20
Purchase #5	$26.83	5.387%	$28.2753	$28.28	$28.30	$28.30
Purchase #6	$64.98	11.650%	$72.5502	$72.55	$72.55	$72.60
Purchase #7	$209.50	7.521%	$225.2565	$225.26	$225.25	$225.30
7 purchase totals =	$557.75		$610.5305	$610.55	$610.55	$610.70