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	$96.79	12.207%	$108.6052	$108.61	$108.60	$108.60
Purchase #2	$73.60	9.846%	$80.8467	$80.85	$80.85	$80.80
Purchase #3	$137.73	10.460%	$152.1366	$152.14	$152.15	$152.10
Purchase #4	$105.43	11.755%	$117.8233	$117.82	$117.80	$117.80
Purchase #5	$87.78	3.489%	$90.8426	$90.84	$90.85	$90.80
Purchase #6	$123.80	5.174%	$130.2054	$130.21	$130.20	$130.20
Purchase #7	$244.45	12.845%	$275.8496	$275.85	$275.85	$275.80
7 purchase totals =	$869.58		$956.3094	$956.32	$956.30	$956.10