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	$129.80	7.314%	$139.2936	$139.29	$139.30	$139.30
Purchase #2	$34.46	4.872%	$36.1389	$36.14	$36.15	$36.10
Purchase #3	$39.59	7.371%	$42.5082	$42.51	$42.50	$42.50
Purchase #4	$143.39	6.391%	$152.5541	$152.55	$152.55	$152.60
Purchase #5	$62.50	13.252%	$70.7825	$70.78	$70.80	$70.80
Purchase #6	$17.99	13.193%	$20.3634	$20.36	$20.35	$20.40
Purchase #7	$100.91	12.149%	$113.1696	$113.17	$113.15	$113.20
7 purchase totals =	$528.64		$574.8103	$574.80	$574.80	$574.90