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	$235.49	12.650%	$265.2795	$265.28	$265.30	$265.30
Purchase #2	$157.25	4.300%	$164.0118	$164.01	$164.00	$164.00
Purchase #3	$44.76	11.257%	$49.7986	$49.80	$49.80	$49.80
Purchase #4	$59.89	11.852%	$66.9882	$66.99	$67.00	$67.00
Purchase #5	$167.69	13.870%	$190.9486	$190.95	$190.95	$190.90
Purchase #6	$156.86	5.784%	$165.9328	$165.93	$165.95	$165.90
Purchase #7	$24.56	12.334%	$27.5892	$27.59	$27.60	$27.60
7 purchase totals =	$846.50		$930.5487	$930.55	$930.60	$930.50