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	$186.87	13.603%	$212.2899	$212.29	$212.30	$212.30
Purchase #2	$78.76	5.605%	$83.1745	$83.17	$83.15	$83.20
Purchase #3	$74.71	7.107%	$80.0196	$80.02	$80.00	$80.00
Purchase #4	$225.28	13.640%	$256.0082	$256.01	$256.00	$256.00
Purchase #5	$240.60	6.286%	$255.7241	$255.72	$255.70	$255.70
Purchase #6	$240.59	6.471%	$256.1586	$256.16	$256.15	$256.20
Purchase #7	$153.34	7.369%	$164.6396	$164.64	$164.65	$164.60
7 purchase totals =	$1,200.15		$1,308.0145	$1,308.01	$1,307.95	$1,308.00