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	$34.72	6.668%	$37.0351	$37.04	$37.05	$37.00
Purchase #2	$243.75	10.835%	$270.1603	$270.16	$270.15	$270.20
Purchase #3	$225.97	9.596%	$247.6541	$247.65	$247.65	$247.70
Purchase #4	$108.26	10.314%	$119.4259	$119.43	$119.45	$119.40
Purchase #5	$196.96	13.522%	$223.5929	$223.59	$223.60	$223.60
Purchase #6	$36.93	4.523%	$38.6003	$38.60	$38.60	$38.60
Purchase #7	$150.58	6.692%	$160.6568	$160.66	$160.65	$160.70
7 purchase totals =	$997.17		$1,097.1254	$1,097.13	$1,097.15	$1,097.20