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	$42.37	3.366%	$43.7962	$43.80	$43.80	$43.80
Purchase #2	$42.85	11.128%	$47.6183	$47.62	$47.60	$47.60
Purchase #3	$113.33	5.804%	$119.9077	$119.91	$119.90	$119.90
Purchase #4	$47.94	10.164%	$52.8126	$52.81	$52.80	$52.80
Purchase #5	$57.30	6.627%	$61.0973	$61.10	$61.10	$61.10
Purchase #6	$200.29	13.704%	$227.7377	$227.74	$227.75	$227.70
Purchase #7	$87.38	12.504%	$98.306	$98.31	$98.30	$98.30
7 purchase totals =	$591.46		$651.2758	$651.29	$651.25	$651.20