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	$241.55	13.358%	$273.8162	$273.82	$273.80	$273.80
Purchase #2	$246.54	3.652%	$255.5436	$255.54	$255.55	$255.50
Purchase #3	$146.56	7.106%	$156.9746	$156.97	$156.95	$157.00
Purchase #4	$20.51	3.773%	$21.2838	$21.28	$21.30	$21.30
Purchase #5	$9.56	10.303%	$10.545	$10.55	$10.55	$10.50
Purchase #6	$6.85	5.625%	$7.2353	$7.24	$7.25	$7.20
Purchase #7	$62.30	7.831%	$67.1787	$67.18	$67.20	$67.20
7 purchase totals =	$733.87		$792.5772	$792.58	$792.60	$792.50