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	$31.50	9.395%	$34.4594	$34.46	$34.45	$34.50
Purchase #2	$103.71	8.297%	$112.3148	$112.31	$112.30	$112.30
Purchase #3	$110.83	11.408%	$123.4735	$123.47	$123.45	$123.50
Purchase #4	$38.82	4.284%	$40.483	$40.48	$40.50	$40.50
Purchase #5	$243.91	9.111%	$266.1326	$266.13	$266.15	$266.10
Purchase #6	$207.25	4.307%	$216.1763	$216.18	$216.20	$216.20
Purchase #7	$8.72	7.431%	$9.368	$9.37	$9.35	$9.40
7 purchase totals =	$744.74		$802.4076	$802.40	$802.40	$802.50