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	$62.96	12.134%	$70.5996	$70.60	$70.60	$70.60
Purchase #2	$99.60	11.460%	$111.0142	$111.01	$111.00	$111.00
Purchase #3	$135.89	12.166%	$152.4224	$152.42	$152.40	$152.40
Purchase #4	$130.85	13.823%	$148.9374	$148.94	$148.95	$148.90
Purchase #5	$60.66	13.536%	$68.8709	$68.87	$68.85	$68.90
Purchase #6	$164.31	9.229%	$179.4742	$179.47	$179.45	$179.50
Purchase #7	$146.74	7.421%	$157.6296	$157.63	$157.65	$157.60
7 purchase totals =	$801.01		$888.9483	$888.94	$888.90	$888.90