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	$123.54	12.782%	$139.3309	$139.33	$139.35	$139.30
Purchase #2	$219.51	10.189%	$241.8759	$241.88	$241.90	$241.90
Purchase #3	$34.41	11.226%	$38.2729	$38.27	$38.25	$38.30
Purchase #4	$217.29	3.194%	$224.2302	$224.23	$224.25	$224.20
Purchase #5	$63.42	5.267%	$66.7603	$66.76	$66.75	$66.80
Purchase #6	$224.62	9.414%	$245.7657	$245.77	$245.75	$245.80
Purchase #7	$104.35	4.500%	$109.0458	$109.05	$109.05	$109.00
7 purchase totals =	$987.14		$1,065.2817	$1,065.29	$1,065.30	$1,065.30