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	$21.39	13.326%	$24.2404	$24.24	$24.25	$24.20
Purchase #2	$101.59	7.605%	$109.3159	$109.32	$109.30	$109.30
Purchase #3	$34.78	11.645%	$38.8301	$38.83	$38.85	$38.80
Purchase #4	$144.60	11.247%	$160.8632	$160.86	$160.85	$160.90
Purchase #5	$140.61	3.689%	$145.7971	$145.80	$145.80	$145.80
Purchase #6	$75.53	13.221%	$85.5158	$85.52	$85.50	$85.50
Purchase #7	$129.60	8.534%	$140.6601	$140.66	$140.65	$140.70
7 purchase totals =	$648.10		$705.2226	$705.23	$705.20	$705.20