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	$165.38	10.292%	$182.4009	$182.40	$182.40	$182.40
Purchase #2	$37.84	4.567%	$39.5682	$39.57	$39.55	$39.60
Purchase #3	$196.63	13.491%	$223.1574	$223.16	$223.15	$223.20
Purchase #4	$51.53	6.735%	$55.0005	$55.00	$55.00	$55.00
Purchase #5	$11.89	5.515%	$12.5457	$12.55	$12.55	$12.50
Purchase #6	$81.73	9.311%	$89.3399	$89.34	$89.35	$89.30
Purchase #7	$15.60	5.486%	$16.4558	$16.46	$16.45	$16.50
7 purchase totals =	$560.60		$618.4684	$618.48	$618.45	$618.50