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	$18.36	13.642%	$20.8647	$20.86	$20.85	$20.90
Purchase #2	$113.94	9.241%	$124.4692	$124.47	$124.45	$124.50
Purchase #3	$111.66	3.238%	$115.2756	$115.28	$115.30	$115.30
Purchase #4	$33.89	11.653%	$37.8392	$37.84	$37.85	$37.80
Purchase #5	$57.87	4.232%	$60.3191	$60.32	$60.30	$60.30
Purchase #6	$10.34	6.565%	$11.0188	$11.02	$11.00	$11.00
Purchase #7	$50.38	6.514%	$53.6618	$53.66	$53.65	$53.70
7 purchase totals =	$396.44		$423.4484	$423.45	$423.40	$423.50