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	$68.31	4.680%	$71.5069	$71.51	$71.50	$71.50
Purchase #2	$223.35	10.510%	$246.8241	$246.82	$246.80	$246.80
Purchase #3	$201.51	11.842%	$225.3728	$225.37	$225.35	$225.40
Purchase #4	$41.57	12.308%	$46.6864	$46.69	$46.70	$46.70
Purchase #5	$129.37	10.705%	$143.2191	$143.22	$143.20	$143.20
Purchase #6	$75.76	6.812%	$80.9208	$80.92	$80.90	$80.90
Purchase #7	$134.79	13.145%	$152.5081	$152.51	$152.50	$152.50
7 purchase totals =	$874.66		$967.0382	$967.04	$966.95	$967.00