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	$27.69	7.562%	$29.7839	$29.78	$29.80	$29.80
Purchase #2	$172.63	13.593%	$196.0956	$196.10	$196.10	$196.10
Purchase #3	$240.98	4.366%	$251.5012	$251.50	$251.50	$251.50
Purchase #4	$192.31	8.393%	$208.4506	$208.45	$208.45	$208.50
Purchase #5	$129.56	3.823%	$134.5131	$134.51	$134.50	$134.50
Purchase #6	$58.65	8.520%	$63.647	$63.65	$63.65	$63.60
Purchase #7	$242.26	13.762%	$275.5998	$275.60	$275.60	$275.60
7 purchase totals =	$1,064.08		$1,159.5912	$1,159.59	$1,159.60	$1,159.60