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	$245.25	10.441%	$270.8566	$270.86	$270.85	$270.90
Purchase #2	$18.88	6.102%	$20.0321	$20.03	$20.05	$20.00
Purchase #3	$42.61	9.396%	$46.6136	$46.61	$46.60	$46.60
Purchase #4	$196.65	8.242%	$212.8579	$212.86	$212.85	$212.90
Purchase #5	$87.26	13.747%	$99.2556	$99.26	$99.25	$99.30
Purchase #6	$147.48	12.211%	$165.4888	$165.49	$165.50	$165.50
Purchase #7	$72.93	10.861%	$80.8509	$80.85	$80.85	$80.90
7 purchase totals =	$811.06		$895.9555	$895.96	$895.95	$896.10