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	$250.38	6.666%	$267.0703	$267.07	$267.05	$267.10
Purchase #2	$224.59	4.154%	$233.9195	$233.92	$233.90	$233.90
Purchase #3	$150.97	6.556%	$160.8676	$160.87	$160.85	$160.90
Purchase #4	$46.36	3.355%	$47.9154	$47.92	$47.90	$47.90
Purchase #5	$123.31	7.160%	$132.139	$132.14	$132.15	$132.10
Purchase #6	$90.45	9.626%	$99.1567	$99.16	$99.15	$99.20
Purchase #7	$231.92	11.707%	$259.0709	$259.07	$259.05	$259.10
7 purchase totals =	$1,117.98		$1,200.1394	$1,200.15	$1,200.05	$1,200.20