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	$226.57	10.644%	$250.6861	$250.69	$250.70	$250.70
Purchase #2	$22.50	10.446%	$24.8504	$24.85	$24.85	$24.90
Purchase #3	$102.92	8.196%	$111.3553	$111.36	$111.35	$111.40
Purchase #4	$217.46	7.180%	$233.0736	$233.07	$233.05	$233.10
Purchase #5	$71.46	9.873%	$78.5152	$78.52	$78.50	$78.50
Purchase #6	$188.89	8.436%	$204.8248	$204.82	$204.80	$204.80
Purchase #7	$90.60	5.444%	$95.5323	$95.53	$95.55	$95.50
7 purchase totals =	$920.40		$998.8377	$998.84	$998.80	$998.90