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	$37.96	10.690%	$42.0179	$42.02	$42.00	$42.00
Purchase #2	$75.48	4.760%	$79.0728	$79.07	$79.05	$79.10
Purchase #3	$159.86	6.295%	$169.9232	$169.92	$169.90	$169.90
Purchase #4	$110.78	11.495%	$123.5142	$123.51	$123.50	$123.50
Purchase #5	$18.42	3.859%	$19.1308	$19.13	$19.15	$19.10
Purchase #6	$164.37	6.145%	$174.4705	$174.47	$174.45	$174.50
Purchase #7	$163.79	9.727%	$179.7219	$179.72	$179.70	$179.70
7 purchase totals =	$730.66		$787.8513	$787.84	$787.75	$787.80