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	$38.96	5.582%	$41.1347	$41.13	$41.15	$41.10
Purchase #2	$244.77	12.409%	$275.1435	$275.14	$275.15	$275.10
Purchase #3	$73.45	13.123%	$83.0888	$83.09	$83.10	$83.10
Purchase #4	$136.36	9.159%	$148.8492	$148.85	$148.85	$148.80
Purchase #5	$92.89	13.498%	$105.4283	$105.43	$105.45	$105.40
Purchase #6	$30.86	11.564%	$34.4287	$34.43	$34.45	$34.40
Purchase #7	$161.96	5.874%	$171.4735	$171.47	$171.45	$171.50
7 purchase totals =	$779.25		$859.5467	$859.54	$859.60	$859.40