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	$64.67	3.451%	$66.9018	$66.90	$66.90	$66.90
Purchase #2	$97.77	7.808%	$105.4039	$105.40	$105.40	$105.40
Purchase #3	$57.45	7.601%	$61.8168	$61.82	$61.80	$61.80
Purchase #4	$205.92	5.353%	$216.9429	$216.94	$216.95	$216.90
Purchase #5	$90.82	11.156%	$100.9519	$100.95	$100.95	$101.00
Purchase #6	$199.50	12.739%	$224.9143	$224.91	$224.90	$224.90
Purchase #7	$141.57	7.351%	$151.9768	$151.98	$152.00	$152.00
7 purchase totals =	$857.70		$928.9084	$928.90	$928.90	$928.90