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	$137.92	3.781%	$143.1348	$143.13	$143.15	$143.10
Purchase #2	$78.87	9.203%	$86.1284	$86.13	$86.15	$86.10
Purchase #3	$18.55	13.707%	$21.0926	$21.09	$21.10	$21.10
Purchase #4	$250.86	9.839%	$275.5421	$275.54	$275.55	$275.50
Purchase #5	$210.81	10.692%	$233.3498	$233.35	$233.35	$233.30
Purchase #6	$160.46	5.612%	$169.465	$169.47	$169.45	$169.50
Purchase #7	$8.44	13.715%	$9.5975	$9.60	$9.60	$9.60
7 purchase totals =	$865.91		$938.3102	$938.31	$938.35	$938.20