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	$250.90	7.277%	$269.158	$269.16	$269.15	$269.20
Purchase #2	$153.68	7.110%	$164.6066	$164.61	$164.60	$164.60
Purchase #3	$5.80	11.545%	$6.4696	$6.47	$6.45	$6.50
Purchase #4	$172.29	13.791%	$196.0505	$196.05	$196.05	$196.10
Purchase #5	$239.87	4.813%	$251.4149	$251.41	$251.40	$251.40
Purchase #6	$55.67	6.714%	$59.4077	$59.41	$59.40	$59.40
Purchase #7	$43.70	5.658%	$46.1725	$46.17	$46.15	$46.20
7 purchase totals =	$921.91		$993.2798	$993.28	$993.20	$993.40