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	$56.82	6.513%	$60.5207	$60.52	$60.50	$60.50
Purchase #2	$145.40	4.552%	$152.0186	$152.02	$152.00	$152.00
Purchase #3	$168.65	5.770%	$178.3811	$178.38	$178.40	$178.40
Purchase #4	$65.30	7.364%	$70.1087	$70.11	$70.10	$70.10
Purchase #5	$94.61	11.809%	$105.7825	$105.78	$105.80	$105.80
Purchase #6	$47.55	5.102%	$49.976	$49.98	$50.00	$50.00
Purchase #7	$86.63	7.230%	$92.8933	$92.89	$92.90	$92.90
7 purchase totals =	$664.96		$709.6809	$709.68	$709.70	$709.70