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	$59.35	12.109%	$66.5367	$66.54	$66.55	$66.50
Purchase #2	$118.95	10.139%	$131.0103	$131.01	$131.00	$131.00
Purchase #3	$230.29	11.145%	$255.9558	$255.96	$255.95	$256.00
Purchase #4	$180.84	5.348%	$190.5113	$190.51	$190.50	$190.50
Purchase #5	$91.41	9.351%	$99.9577	$99.96	$99.95	$100.00
Purchase #6	$181.81	12.628%	$204.769	$204.77	$204.75	$204.80
Purchase #7	$201.66	7.184%	$216.1473	$216.15	$216.15	$216.10
7 purchase totals =	$1,064.31		$1,164.8881	$1,164.90	$1,164.85	$1,164.90