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	$231.97	10.201%	$255.6333	$255.63	$255.65	$255.60
Purchase #2	$79.47	8.151%	$85.9476	$85.95	$85.95	$85.90
Purchase #3	$122.80	6.253%	$130.4787	$130.48	$130.50	$130.50
Purchase #4	$70.86	5.615%	$74.8388	$74.84	$74.85	$74.80
Purchase #5	$233.55	5.654%	$246.7549	$246.75	$246.75	$246.80
Purchase #6	$87.34	3.624%	$90.5052	$90.51	$90.50	$90.50
Purchase #7	$192.32	8.374%	$208.4249	$208.42	$208.40	$208.40
7 purchase totals =	$1,018.31		$1,092.5834	$1,092.58	$1,092.60	$1,092.50