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	$51.65	13.329%	$58.5344	$58.53	$58.55	$58.50
Purchase #2	$65.44	10.689%	$72.4349	$72.43	$72.45	$72.40
Purchase #3	$113.93	9.251%	$124.4697	$124.47	$124.45	$124.50
Purchase #4	$197.85	12.553%	$222.6861	$222.69	$222.70	$222.70
Purchase #5	$68.85	5.678%	$72.7593	$72.76	$72.75	$72.80
Purchase #6	$103.78	12.600%	$116.8563	$116.86	$116.85	$116.90
Purchase #7	$217.57	6.592%	$231.9122	$231.91	$231.90	$231.90
7 purchase totals =	$819.07		$899.6529	$899.65	$899.65	$899.70