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	$168.98	6.169%	$179.4044	$179.40	$179.40	$179.40
Purchase #2	$80.90	3.611%	$83.8213	$83.82	$83.80	$83.80
Purchase #3	$88.46	11.549%	$98.6762	$98.68	$98.70	$98.70
Purchase #4	$134.95	9.763%	$148.1252	$148.13	$148.15	$148.10
Purchase #5	$158.65	3.504%	$164.2091	$164.21	$164.20	$164.20
Purchase #6	$151.88	4.772%	$159.1277	$159.13	$159.15	$159.10
Purchase #7	$56.40	5.373%	$59.4304	$59.43	$59.45	$59.40
7 purchase totals =	$840.22		$892.7943	$892.80	$892.85	$892.70