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	$25.91	13.791%	$29.4832	$29.48	$29.50	$29.50
Purchase #2	$216.98	7.606%	$233.4835	$233.48	$233.50	$233.50
Purchase #3	$45.75	12.508%	$51.4724	$51.47	$51.45	$51.50
Purchase #4	$162.73	4.718%	$170.4076	$170.41	$170.40	$170.40
Purchase #5	$156.41	8.777%	$170.1381	$170.14	$170.15	$170.10
Purchase #6	$78.61	4.635%	$82.2536	$82.25	$82.25	$82.30
Purchase #7	$137.64	11.726%	$153.7797	$153.78	$153.80	$153.80
7 purchase totals =	$824.03		$891.0181	$891.01	$891.05	$891.10