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	$35.87	4.526%	$37.4935	$37.49	$37.50	$37.50
Purchase #2	$172.80	12.532%	$194.4553	$194.46	$194.45	$194.50
Purchase #3	$107.30	10.846%	$118.9378	$118.94	$118.95	$118.90
Purchase #4	$68.28	8.188%	$73.8708	$73.87	$73.85	$73.90
Purchase #5	$87.36	4.301%	$91.1174	$91.12	$91.10	$91.10
Purchase #6	$115.54	6.843%	$123.4464	$123.45	$123.45	$123.40
Purchase #7	$222.58	13.123%	$251.7892	$251.79	$251.80	$251.80
7 purchase totals =	$809.73		$891.1104	$891.12	$891.10	$891.10