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	$7.42	13.431%	$8.4166	$8.42	$8.40	$8.40
Purchase #2	$50.53	7.455%	$54.297	$54.30	$54.30	$54.30
Purchase #3	$186.79	13.739%	$212.4531	$212.45	$212.45	$212.50
Purchase #4	$98.63	13.636%	$112.0792	$112.08	$112.10	$112.10
Purchase #5	$132.90	3.773%	$137.9143	$137.91	$137.90	$137.90
Purchase #6	$113.69	12.157%	$127.5113	$127.51	$127.50	$127.50
Purchase #7	$11.44	13.753%	$13.0133	$13.01	$13.00	$13.00
7 purchase totals =	$601.40		$665.6848	$665.68	$665.65	$665.70