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	$85.68	5.346%	$90.2605	$90.26	$90.25	$90.30
Purchase #2	$56.31	3.657%	$58.3693	$58.37	$58.35	$58.40
Purchase #3	$121.85	7.662%	$131.1861	$131.19	$131.20	$131.20
Purchase #4	$172.50	4.459%	$180.1918	$180.19	$180.20	$180.20
Purchase #5	$235.89	8.445%	$255.8109	$255.81	$255.80	$255.80
Purchase #6	$217.97	11.422%	$242.8665	$242.87	$242.85	$242.90
Purchase #7	$129.57	13.700%	$147.3211	$147.32	$147.30	$147.30
7 purchase totals =	$1,019.77		$1,106.0062	$1,106.01	$1,105.95	$1,106.10