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	$26.37	8.463%	$28.6017	$28.60	$28.60	$28.60
Purchase #2	$159.31	9.441%	$174.3505	$174.35	$174.35	$174.40
Purchase #3	$60.89	9.566%	$66.7147	$66.71	$66.70	$66.70
Purchase #4	$37.69	8.359%	$40.8405	$40.84	$40.85	$40.80
Purchase #5	$18.44	11.730%	$20.603	$20.60	$20.60	$20.60
Purchase #6	$213.45	9.551%	$233.8366	$233.84	$233.85	$233.80
Purchase #7	$158.61	11.494%	$176.8406	$176.84	$176.85	$176.80
7 purchase totals =	$674.76		$741.7876	$741.78	$741.80	$741.70