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	$18.90	7.426%	$20.3035	$20.30	$20.30	$20.30
Purchase #2	$140.54	4.273%	$146.5453	$146.55	$146.55	$146.50
Purchase #3	$129.85	6.219%	$137.9254	$137.93	$137.95	$137.90
Purchase #4	$59.25	9.871%	$65.0986	$65.10	$65.10	$65.10
Purchase #5	$148.28	13.846%	$168.8108	$168.81	$168.80	$168.80
Purchase #6	$95.47	11.635%	$106.5779	$106.58	$106.60	$106.60
Purchase #7	$103.77	10.430%	$114.5932	$114.59	$114.60	$114.60
7 purchase totals =	$696.06		$759.8547	$759.86	$759.90	$759.80