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	$19.30	11.727%	$21.5633	$21.56	$21.55	$21.60
Purchase #2	$97.34	13.166%	$110.1558	$110.16	$110.15	$110.20
Purchase #3	$29.96	12.114%	$33.5894	$33.59	$33.60	$33.60
Purchase #4	$215.66	5.528%	$227.5817	$227.58	$227.60	$227.60
Purchase #5	$205.54	3.389%	$212.5058	$212.51	$212.50	$212.50
Purchase #6	$70.66	5.195%	$74.3308	$74.33	$74.35	$74.30
Purchase #7	$81.78	4.539%	$85.492	$85.49	$85.50	$85.50
7 purchase totals =	$720.24		$765.2188	$765.22	$765.25	$765.30