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	$15.27	4.105%	$15.8968	$15.90	$15.90	$15.90
Purchase #2	$214.90	3.338%	$222.0734	$222.07	$222.05	$222.10
Purchase #3	$105.45	6.777%	$112.5963	$112.60	$112.60	$112.60
Purchase #4	$87.86	6.196%	$93.3038	$93.30	$93.30	$93.30
Purchase #5	$138.91	6.240%	$147.578	$147.58	$147.60	$147.60
Purchase #6	$111.69	5.234%	$117.5359	$117.54	$117.55	$117.50
Purchase #7	$152.67	8.459%	$165.5844	$165.58	$165.60	$165.60
7 purchase totals =	$826.75		$874.5686	$874.57	$874.60	$874.60