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	$199.39	10.773%	$220.8703	$220.87	$220.85	$220.90
Purchase #2	$138.38	3.624%	$143.3949	$143.39	$143.40	$143.40
Purchase #3	$45.36	13.296%	$51.3911	$51.39	$51.40	$51.40
Purchase #4	$55.71	6.137%	$59.1289	$59.13	$59.15	$59.10
Purchase #5	$152.55	3.804%	$158.353	$158.35	$158.35	$158.40
Purchase #6	$207.69	10.376%	$229.2399	$229.24	$229.25	$229.20
Purchase #7	$81.96	8.492%	$88.92	$88.92	$88.90	$88.90
7 purchase totals =	$881.04		$951.2981	$951.29	$951.30	$951.30