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	$9.37	13.135%	$10.6007	$10.60	$10.60	$10.60
Purchase #2	$231.57	9.643%	$253.9003	$253.90	$253.90	$253.90
Purchase #3	$93.52	7.338%	$100.3825	$100.38	$100.40	$100.40
Purchase #4	$53.86	6.690%	$57.4632	$57.46	$57.45	$57.50
Purchase #5	$103.35	3.129%	$106.5838	$106.58	$106.60	$106.60
Purchase #6	$242.85	12.524%	$273.2645	$273.26	$273.25	$273.30
Purchase #7	$20.59	10.821%	$22.818	$22.82	$22.80	$22.80
7 purchase totals =	$755.11		$825.0130	$825.00	$825.00	$825.10