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	$77.53	7.164%	$83.0842	$83.08	$83.10	$83.10
Purchase #2	$162.84	4.827%	$170.7003	$170.70	$170.70	$170.70
Purchase #3	$97.28	3.392%	$100.5797	$100.58	$100.60	$100.60
Purchase #4	$52.99	3.314%	$54.7461	$54.75	$54.75	$54.70
Purchase #5	$23.25	4.650%	$24.3311	$24.33	$24.35	$24.30
Purchase #6	$116.33	9.460%	$127.3348	$127.33	$127.35	$127.30
Purchase #7	$64.64	11.395%	$72.0057	$72.01	$72.00	$72.00
7 purchase totals =	$594.86		$632.7819	$632.78	$632.85	$632.70