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	$176.82	6.716%	$188.6952	$188.70	$188.70	$188.70
Purchase #2	$55.45	7.463%	$59.5882	$59.59	$59.60	$59.60
Purchase #3	$245.42	4.370%	$256.1449	$256.14	$256.15	$256.10
Purchase #4	$218.42	10.843%	$242.1033	$242.10	$242.10	$242.10
Purchase #5	$140.86	5.130%	$148.0861	$148.09	$148.10	$148.10
Purchase #6	$68.92	7.855%	$74.3337	$74.33	$74.35	$74.30
Purchase #7	$73.64	9.204%	$80.4178	$80.42	$80.40	$80.40
7 purchase totals =	$979.53		$1,049.3692	$1,049.37	$1,049.40	$1,049.30