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	$22.30	11.318%	$24.8239	$24.82	$24.80	$24.80
Purchase #2	$115.40	10.814%	$127.8794	$127.88	$127.90	$127.90
Purchase #3	$119.36	3.595%	$123.651	$123.65	$123.65	$123.70
Purchase #4	$182.31	10.139%	$200.7944	$200.79	$200.80	$200.80
Purchase #5	$15.50	12.550%	$17.4453	$17.45	$17.45	$17.40
Purchase #6	$226.67	13.269%	$256.7468	$256.75	$256.75	$256.70
Purchase #7	$233.86	5.720%	$247.2368	$247.24	$247.25	$247.20
7 purchase totals =	$915.40		$998.5776	$998.58	$998.60	$998.50