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	$101.25	13.117%	$114.531	$114.53	$114.55	$114.50
Purchase #2	$134.59	3.707%	$139.5793	$139.58	$139.60	$139.60
Purchase #3	$43.72	13.839%	$49.7704	$49.77	$49.75	$49.80
Purchase #4	$146.70	12.317%	$164.769	$164.77	$164.75	$164.80
Purchase #5	$166.52	7.679%	$179.3071	$179.31	$179.30	$179.30
Purchase #6	$232.44	6.266%	$247.0047	$247.00	$247.00	$247.00
Purchase #7	$56.56	10.564%	$62.535	$62.54	$62.55	$62.50
7 purchase totals =	$881.78		$957.4965	$957.50	$957.50	$957.50