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	$136.54	7.313%	$146.5252	$146.53	$146.55	$146.50
Purchase #2	$100.38	12.340%	$112.7669	$112.77	$112.75	$112.80
Purchase #3	$185.25	10.814%	$205.2829	$205.28	$205.30	$205.30
Purchase #4	$53.94	12.210%	$60.5261	$60.53	$60.55	$60.50
Purchase #5	$20.50	9.363%	$22.4194	$22.42	$22.40	$22.40
Purchase #6	$210.32	13.493%	$238.6985	$238.70	$238.70	$238.70
Purchase #7	$45.80	13.644%	$52.049	$52.05	$52.05	$52.00
7 purchase totals =	$752.73		$838.2680	$838.28	$838.30	$838.20