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	$61.53	4.306%	$64.1795	$64.18	$64.20	$64.20
Purchase #2	$61.86	7.439%	$66.4618	$66.46	$66.45	$66.50
Purchase #3	$91.30	13.480%	$103.6072	$103.61	$103.60	$103.60
Purchase #4	$125.31	11.759%	$140.0452	$140.05	$140.05	$140.00
Purchase #5	$41.81	11.840%	$46.7603	$46.76	$46.75	$46.80
Purchase #6	$162.25	5.167%	$170.6335	$170.63	$170.65	$170.60
Purchase #7	$79.47	12.337%	$89.2742	$89.27	$89.25	$89.30
7 purchase totals =	$623.53		$680.9617	$680.96	$680.95	$681.00