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	$227.28	12.743%	$256.2423	$256.24	$256.25	$256.20
Purchase #2	$180.25	9.241%	$196.9069	$196.91	$196.90	$196.90
Purchase #3	$49.94	5.366%	$52.6198	$52.62	$52.60	$52.60
Purchase #4	$66.72	7.276%	$71.5745	$71.57	$71.55	$71.60
Purchase #5	$52.80	9.300%	$57.7104	$57.71	$57.70	$57.70
Purchase #6	$44.47	9.135%	$48.5323	$48.53	$48.55	$48.50
Purchase #7	$178.64	3.154%	$184.2743	$184.27	$184.25	$184.30
7 purchase totals =	$800.10		$867.8605	$867.85	$867.80	$867.80