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	$50.58	8.452%	$54.855	$54.86	$54.85	$54.90
Purchase #2	$158.48	12.487%	$178.2694	$178.27	$178.25	$178.30
Purchase #3	$166.38	4.629%	$174.0817	$174.08	$174.10	$174.10
Purchase #4	$165.37	10.314%	$182.4263	$182.43	$182.45	$182.40
Purchase #5	$52.42	8.440%	$56.8442	$56.84	$56.85	$56.80
Purchase #6	$158.29	13.780%	$180.1024	$180.10	$180.10	$180.10
Purchase #7	$95.58	5.347%	$100.6907	$100.69	$100.70	$100.70
7 purchase totals =	$847.10		$927.2697	$927.27	$927.30	$927.30