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	$29.83	5.809%	$31.5628	$31.56	$31.55	$31.60
Purchase #2	$134.58	10.327%	$148.4781	$148.48	$148.50	$148.50
Purchase #3	$122.48	3.870%	$127.22	$127.22	$127.20	$127.20
Purchase #4	$35.51	5.249%	$37.3739	$37.37	$37.35	$37.40
Purchase #5	$44.83	9.185%	$48.9476	$48.95	$48.95	$48.90
Purchase #6	$195.41	7.711%	$210.4781	$210.48	$210.50	$210.50
Purchase #7	$43.51	4.624%	$45.5219	$45.52	$45.50	$45.50
7 purchase totals =	$606.15		$649.5824	$649.58	$649.55	$649.60