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	$129.58	8.275%	$140.3027	$140.30	$140.30	$140.30
Purchase #2	$117.51	5.387%	$123.8403	$123.84	$123.85	$123.80
Purchase #3	$53.77	11.389%	$59.8939	$59.89	$59.90	$59.90
Purchase #4	$46.98	13.698%	$53.4153	$53.42	$53.40	$53.40
Purchase #5	$52.57	7.413%	$56.467	$56.47	$56.45	$56.50
Purchase #6	$113.36	6.683%	$120.9358	$120.94	$120.95	$120.90
Purchase #7	$164.87	11.573%	$183.9504	$183.95	$183.95	$184.00
7 purchase totals =	$678.64		$738.8054	$738.81	$738.80	$738.80