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	$68.72	13.815%	$78.2137	$78.21	$78.20	$78.20
Purchase #2	$117.52	4.870%	$123.2432	$123.24	$123.25	$123.20
Purchase #3	$140.66	7.240%	$150.8438	$150.84	$150.85	$150.80
Purchase #4	$52.44	5.739%	$55.4495	$55.45	$55.45	$55.40
Purchase #5	$108.55	10.871%	$120.3505	$120.35	$120.35	$120.40
Purchase #6	$109.64	12.209%	$123.0259	$123.03	$123.05	$123.00
Purchase #7	$79.29	10.705%	$87.778	$87.78	$87.80	$87.80
7 purchase totals =	$676.82		$738.9046	$738.90	$738.95	$738.80