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	$36.28	5.778%	$38.3763	$38.38	$38.40	$38.40
Purchase #2	$146.93	9.186%	$160.427	$160.43	$160.45	$160.40
Purchase #3	$123.63	7.428%	$132.8132	$132.81	$132.80	$132.80
Purchase #4	$247.36	3.541%	$256.119	$256.12	$256.10	$256.10
Purchase #5	$127.83	5.465%	$134.8159	$134.82	$134.80	$134.80
Purchase #6	$63.72	13.201%	$72.1317	$72.13	$72.15	$72.10
Purchase #7	$26.69	11.240%	$29.69	$29.69	$29.70	$29.70
7 purchase totals =	$772.44		$824.3731	$824.38	$824.40	$824.30