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	$150.36	12.285%	$168.8317	$168.83	$168.85	$168.80
Purchase #2	$215.95	9.643%	$236.7741	$236.77	$236.75	$236.80
Purchase #3	$109.34	13.620%	$124.2321	$124.23	$124.25	$124.20
Purchase #4	$154.70	13.681%	$175.8645	$175.86	$175.85	$175.90
Purchase #5	$104.87	8.242%	$113.5134	$113.51	$113.50	$113.50
Purchase #6	$44.68	13.274%	$50.6108	$50.61	$50.60	$50.60
Purchase #7	$83.51	6.845%	$89.2263	$89.23	$89.25	$89.20
7 purchase totals =	$863.41		$959.0529	$959.04	$959.05	$959.00