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	$44.55	8.340%	$48.2655	$48.27	$48.25	$48.30
Purchase #2	$74.98	8.516%	$81.3653	$81.37	$81.35	$81.40
Purchase #3	$162.87	10.812%	$180.4795	$180.48	$180.50	$180.50
Purchase #4	$165.88	5.748%	$175.4148	$175.41	$175.40	$175.40
Purchase #5	$12.82	7.394%	$13.7679	$13.77	$13.75	$13.80
Purchase #6	$76.57	5.483%	$80.7683	$80.77	$80.75	$80.80
Purchase #7	$93.79	7.180%	$100.5241	$100.52	$100.50	$100.50
7 purchase totals =	$631.46		$680.5854	$680.59	$680.50	$680.70