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	$85.30	10.752%	$94.4715	$94.47	$94.45	$94.50
Purchase #2	$176.49	13.217%	$199.8167	$199.82	$199.80	$199.80
Purchase #3	$216.56	8.136%	$234.1793	$234.18	$234.20	$234.20
Purchase #4	$132.86	10.115%	$146.2988	$146.30	$146.30	$146.30
Purchase #5	$32.93	8.834%	$35.839	$35.84	$35.85	$35.80
Purchase #6	$90.75	11.120%	$100.8414	$100.84	$100.85	$100.80
Purchase #7	$165.26	4.139%	$172.1001	$172.10	$172.10	$172.10
7 purchase totals =	$900.15		$983.5468	$983.55	$983.55	$983.50