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	$72.81	13.812%	$82.8665	$82.87	$82.85	$82.90
Purchase #2	$34.26	13.713%	$38.9581	$38.96	$38.95	$39.00
Purchase #3	$42.83	13.822%	$48.75	$48.75	$48.75	$48.80
Purchase #4	$204.29	4.596%	$213.6792	$213.68	$213.70	$213.70
Purchase #5	$108.45	7.333%	$116.4026	$116.40	$116.40	$116.40
Purchase #6	$54.61	12.244%	$61.2964	$61.30	$61.30	$61.30
Purchase #7	$67.27	13.667%	$76.4638	$76.46	$76.45	$76.50
7 purchase totals =	$584.52		$638.4166	$638.42	$638.40	$638.60