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	$143.56	3.638%	$148.7827	$148.78	$148.80	$148.80
Purchase #2	$67.89	9.184%	$74.125	$74.13	$74.15	$74.10
Purchase #3	$154.39	11.666%	$172.4011	$172.40	$172.40	$172.40
Purchase #4	$16.38	10.623%	$18.12	$18.12	$18.10	$18.10
Purchase #5	$38.46	5.436%	$40.5507	$40.55	$40.55	$40.60
Purchase #6	$25.75	5.374%	$27.1338	$27.13	$27.15	$27.10
Purchase #7	$219.95	3.407%	$227.4437	$227.44	$227.45	$227.40
7 purchase totals =	$666.38		$708.5570	$708.55	$708.60	$708.50