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	$103.45	13.546%	$117.4633	$117.46	$117.45	$117.50
Purchase #2	$166.74	13.663%	$189.5217	$189.52	$189.50	$189.50
Purchase #3	$89.78	9.803%	$98.5811	$98.58	$98.60	$98.60
Purchase #4	$123.36	4.343%	$128.7175	$128.72	$128.70	$128.70
Purchase #5	$74.94	4.252%	$78.1264	$78.13	$78.15	$78.10
Purchase #6	$186.88	9.468%	$204.5738	$204.57	$204.55	$204.60
Purchase #7	$45.86	5.402%	$48.3374	$48.34	$48.35	$48.30
7 purchase totals =	$791.01		$865.3212	$865.32	$865.30	$865.30