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	$108.89	7.806%	$117.39	$117.39	$117.40	$117.40
Purchase #2	$131.53	13.105%	$148.767	$148.77	$148.75	$148.80
Purchase #3	$120.58	9.160%	$131.6251	$131.63	$131.65	$131.60
Purchase #4	$176.46	4.680%	$184.7183	$184.72	$184.70	$184.70
Purchase #5	$18.32	11.558%	$20.4374	$20.44	$20.45	$20.40
Purchase #6	$76.62	9.394%	$83.8177	$83.82	$83.80	$83.80
Purchase #7	$146.33	6.319%	$155.5766	$155.58	$155.60	$155.60
7 purchase totals =	$778.73		$842.3321	$842.35	$842.35	$842.30