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	$21.98	13.108%	$24.8611	$24.86	$24.85	$24.90
Purchase #2	$234.27	13.666%	$266.2853	$266.29	$266.30	$266.30
Purchase #3	$134.30	11.547%	$149.8076	$149.81	$149.80	$149.80
Purchase #4	$215.88	8.215%	$233.6145	$233.61	$233.60	$233.60
Purchase #5	$235.42	8.257%	$254.8586	$254.86	$254.85	$254.90
Purchase #6	$153.52	11.108%	$170.573	$170.57	$170.55	$170.60
Purchase #7	$64.85	12.504%	$72.9588	$72.96	$72.95	$73.00
7 purchase totals =	$1,060.22		$1,172.9589	$1,172.96	$1,172.90	$1,173.10