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	$170.29	5.790%	$180.1498	$180.15	$180.15	$180.10
Purchase #2	$176.51	5.106%	$185.5226	$185.52	$185.50	$185.50
Purchase #3	$164.32	9.540%	$179.9961	$180.00	$180.00	$180.00
Purchase #4	$240.89	11.548%	$268.708	$268.71	$268.70	$268.70
Purchase #5	$56.57	4.614%	$59.1801	$59.18	$59.20	$59.20
Purchase #6	$10.59	9.224%	$11.5668	$11.57	$11.55	$11.60
Purchase #7	$48.42	13.263%	$54.8419	$54.84	$54.85	$54.80
7 purchase totals =	$867.59		$939.9653	$939.97	$939.95	$939.90