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	$34.91	8.536%	$37.8899	$37.89	$37.90	$37.90
Purchase #2	$46.55	4.265%	$48.5354	$48.54	$48.55	$48.50
Purchase #3	$42.38	3.771%	$43.9781	$43.98	$44.00	$44.00
Purchase #4	$155.30	10.277%	$171.2602	$171.26	$171.25	$171.30
Purchase #5	$77.87	4.658%	$81.4972	$81.50	$81.50	$81.50
Purchase #6	$163.97	5.684%	$173.2901	$173.29	$173.30	$173.30
Purchase #7	$82.99	10.855%	$91.9986	$92.00	$92.00	$92.00
7 purchase totals =	$603.97		$648.4495	$648.46	$648.50	$648.50