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	$105.79	3.399%	$109.3858	$109.39	$109.40	$109.40
Purchase #2	$96.25	11.175%	$107.0059	$107.01	$107.00	$107.00
Purchase #3	$89.55	3.690%	$92.8544	$92.85	$92.85	$92.90
Purchase #4	$183.33	13.754%	$208.5452	$208.55	$208.55	$208.50
Purchase #5	$86.71	5.447%	$91.4331	$91.43	$91.45	$91.40
Purchase #6	$57.51	12.667%	$64.7948	$64.79	$64.80	$64.80
Purchase #7	$116.28	11.866%	$130.0778	$130.08	$130.10	$130.10
7 purchase totals =	$735.42		$804.0970	$804.10	$804.15	$804.10