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	$18.41	13.305%	$20.8595	$20.86	$20.85	$20.90
Purchase #2	$5.60	10.612%	$6.1943	$6.19	$6.20	$6.20
Purchase #3	$85.33	5.757%	$90.2424	$90.24	$90.25	$90.20
Purchase #4	$103.72	4.419%	$108.3034	$108.30	$108.30	$108.30
Purchase #5	$103.34	7.685%	$111.2817	$111.28	$111.30	$111.30
Purchase #6	$87.72	10.186%	$96.6552	$96.66	$96.65	$96.70
Purchase #7	$57.59	6.690%	$61.4428	$61.44	$61.45	$61.40
7 purchase totals =	$461.71		$494.9793	$494.97	$495.00	$495.00