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	$18.80	10.663%	$20.8046	$20.80	$20.80	$20.80
Purchase #2	$217.56	12.353%	$244.4352	$244.44	$244.45	$244.40
Purchase #3	$24.37	12.147%	$27.3302	$27.33	$27.35	$27.30
Purchase #4	$9.63	12.727%	$10.8556	$10.86	$10.85	$10.90
Purchase #5	$108.32	9.698%	$118.8249	$118.82	$118.80	$118.80
Purchase #6	$177.83	6.238%	$188.923	$188.92	$188.90	$188.90
Purchase #7	$203.71	13.578%	$231.3697	$231.37	$231.35	$231.40
7 purchase totals =	$760.22		$842.5432	$842.54	$842.50	$842.50