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	$75.26	6.317%	$80.0142	$80.01	$80.00	$80.00
Purchase #2	$191.75	13.852%	$218.3112	$218.31	$218.30	$218.30
Purchase #3	$111.47	10.581%	$123.2646	$123.26	$123.25	$123.30
Purchase #4	$47.45	5.152%	$49.8946	$49.89	$49.90	$49.90
Purchase #5	$245.58	8.367%	$266.1277	$266.13	$266.15	$266.10
Purchase #6	$179.28	8.537%	$194.5851	$194.59	$194.60	$194.60
Purchase #7	$91.79	8.502%	$99.594	$99.59	$99.60	$99.60
7 purchase totals =	$942.58		$1,031.7914	$1,031.78	$1,031.80	$1,031.80