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	$181.93	4.379%	$189.8967	$189.90	$189.90	$189.90
Purchase #2	$60.51	4.130%	$63.0091	$63.01	$63.00	$63.00
Purchase #3	$125.73	13.422%	$142.6055	$142.61	$142.60	$142.60
Purchase #4	$149.35	12.302%	$167.723	$167.72	$167.70	$167.70
Purchase #5	$153.48	3.120%	$158.2686	$158.27	$158.25	$158.30
Purchase #6	$83.74	10.428%	$92.4724	$92.47	$92.45	$92.50
Purchase #7	$242.60	13.118%	$274.4243	$274.42	$274.40	$274.40
7 purchase totals =	$997.34		$1,088.3996	$1,088.40	$1,088.30	$1,088.40