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	$178.40	3.536%	$184.7082	$184.71	$184.70	$184.70
Purchase #2	$34.32	7.502%	$36.8947	$36.89	$36.90	$36.90
Purchase #3	$102.81	6.853%	$109.8556	$109.86	$109.85	$109.90
Purchase #4	$167.82	6.779%	$179.1965	$179.20	$179.20	$179.20
Purchase #5	$52.65	6.784%	$56.2218	$56.22	$56.20	$56.20
Purchase #6	$222.72	9.523%	$243.9296	$243.93	$243.95	$243.90
Purchase #7	$160.91	4.724%	$168.5114	$168.51	$168.50	$168.50
7 purchase totals =	$919.63		$979.3178	$979.32	$979.30	$979.30