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	$90.72	9.650%	$99.4745	$99.47	$99.45	$99.50
Purchase #2	$148.87	13.868%	$169.5153	$169.52	$169.50	$169.50
Purchase #3	$250.65	10.618%	$277.264	$277.26	$277.25	$277.30
Purchase #4	$126.30	8.803%	$137.4182	$137.42	$137.40	$137.40
Purchase #5	$21.83	12.800%	$24.6242	$24.62	$24.60	$24.60
Purchase #6	$52.89	9.833%	$58.0907	$58.09	$58.10	$58.10
Purchase #7	$162.39	10.859%	$180.0239	$180.02	$180.00	$180.00
7 purchase totals =	$853.65		$946.4108	$946.40	$946.30	$946.40