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	$133.90	12.474%	$150.6027	$150.60	$150.60	$150.60
Purchase #2	$135.71	5.329%	$142.942	$142.94	$142.95	$142.90
Purchase #3	$129.86	5.106%	$136.4907	$136.49	$136.50	$136.50
Purchase #4	$145.94	12.727%	$164.5138	$164.51	$164.50	$164.50
Purchase #5	$217.25	6.530%	$231.4364	$231.44	$231.45	$231.40
Purchase #6	$84.41	6.770%	$90.1246	$90.12	$90.10	$90.10
Purchase #7	$224.58	12.566%	$252.8007	$252.80	$252.80	$252.80
7 purchase totals =	$1,071.65		$1,168.9109	$1,168.90	$1,168.90	$1,168.80