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	$18.42	6.495%	$19.6164	$19.62	$19.60	$19.60
Purchase #2	$12.37	6.355%	$13.1561	$13.16	$13.15	$13.20
Purchase #3	$32.42	13.384%	$36.7591	$36.76	$36.75	$36.80
Purchase #4	$152.81	8.391%	$165.6323	$165.63	$165.65	$165.60
Purchase #5	$145.25	13.264%	$164.516	$164.52	$164.50	$164.50
Purchase #6	$81.70	9.399%	$89.379	$89.38	$89.40	$89.40
Purchase #7	$53.69	3.703%	$55.6781	$55.68	$55.70	$55.70
7 purchase totals =	$496.66		$544.7370	$544.75	$544.75	$544.80