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	$19.68	9.692%	$21.5874	$21.59	$21.60	$21.60
Purchase #2	$40.46	5.163%	$42.5489	$42.55	$42.55	$42.50
Purchase #3	$15.60	4.373%	$16.2822	$16.28	$16.30	$16.30
Purchase #4	$21.84	12.400%	$24.5482	$24.55	$24.55	$24.50
Purchase #5	$33.50	6.674%	$35.7358	$35.74	$35.75	$35.70
Purchase #6	$56.81	13.222%	$64.3214	$64.32	$64.30	$64.30
Purchase #7	$205.90	8.706%	$223.8257	$223.83	$223.85	$223.80
7 purchase totals =	$393.79		$428.8496	$428.86	$428.90	$428.70