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	$65.96	10.390%	$72.8132	$72.81	$72.80	$72.80
Purchase #2	$78.75	9.840%	$86.499	$86.50	$86.50	$86.50
Purchase #3	$230.96	10.415%	$255.0145	$255.01	$255.00	$255.00
Purchase #4	$184.51	13.124%	$208.7251	$208.73	$208.75	$208.70
Purchase #5	$69.40	4.347%	$72.4168	$72.42	$72.40	$72.40
Purchase #6	$28.64	13.620%	$32.5408	$32.54	$32.55	$32.50
Purchase #7	$248.72	5.812%	$263.1756	$263.18	$263.20	$263.20
7 purchase totals =	$906.94		$991.1850	$991.19	$991.20	$991.10