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	$16.85	5.528%	$17.7815	$17.78	$17.80	$17.80
Purchase #2	$200.68	10.565%	$221.8818	$221.88	$221.90	$221.90
Purchase #3	$44.61	4.739%	$46.7241	$46.72	$46.70	$46.70
Purchase #4	$29.50	8.607%	$32.0391	$32.04	$32.05	$32.00
Purchase #5	$149.83	11.624%	$167.2462	$167.25	$167.25	$167.20
Purchase #6	$28.96	13.336%	$32.8221	$32.82	$32.80	$32.80
Purchase #7	$33.92	4.195%	$35.3429	$35.34	$35.35	$35.30
7 purchase totals =	$504.35		$553.8377	$553.83	$553.85	$553.70