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	$25.94	4.226%	$27.0362	$27.04	$27.05	$27.00
Purchase #2	$233.65	9.329%	$255.4472	$255.45	$255.45	$255.40
Purchase #3	$64.25	12.455%	$72.2523	$72.25	$72.25	$72.30
Purchase #4	$139.46	13.747%	$158.6316	$158.63	$158.65	$158.60
Purchase #5	$83.58	10.225%	$92.1261	$92.13	$92.15	$92.10
Purchase #6	$144.39	10.449%	$159.4773	$159.48	$159.50	$159.50
Purchase #7	$63.90	4.390%	$66.7052	$66.71	$66.70	$66.70
7 purchase totals =	$755.17		$831.6759	$831.69	$831.75	$831.60