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	$77.69	11.739%	$86.81	$86.81	$86.80	$86.80
Purchase #2	$60.77	7.575%	$65.3733	$65.37	$65.35	$65.40
Purchase #3	$72.46	10.707%	$80.2183	$80.22	$80.20	$80.20
Purchase #4	$154.60	3.183%	$159.5209	$159.52	$159.50	$159.50
Purchase #5	$88.34	6.271%	$93.8798	$93.88	$93.90	$93.90
Purchase #6	$57.92	4.553%	$60.5571	$60.56	$60.55	$60.60
Purchase #7	$91.60	9.703%	$100.4879	$100.49	$100.50	$100.50
7 purchase totals =	$603.38		$646.8473	$646.85	$646.80	$646.90