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	$10.90	12.295%	$12.2402	$12.24	$12.25	$12.20
Purchase #2	$129.34	7.162%	$138.6033	$138.60	$138.60	$138.60
Purchase #3	$46.87	4.173%	$48.8259	$48.83	$48.85	$48.80
Purchase #4	$30.93	8.308%	$33.4997	$33.50	$33.50	$33.50
Purchase #5	$188.28	4.234%	$196.2518	$196.25	$196.25	$196.30
Purchase #6	$160.33	3.647%	$166.1772	$166.18	$166.20	$166.20
Purchase #7	$33.26	11.650%	$37.1348	$37.13	$37.15	$37.10
7 purchase totals =	$599.91		$632.7329	$632.73	$632.80	$632.70