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	$104.59	3.551%	$108.304	$108.30	$108.30	$108.30
Purchase #2	$90.50	13.375%	$102.6044	$102.60	$102.60	$102.60
Purchase #3	$154.80	9.202%	$169.0447	$169.04	$169.05	$169.00
Purchase #4	$76.80	4.521%	$80.2721	$80.27	$80.25	$80.30
Purchase #5	$25.60	11.697%	$28.5944	$28.59	$28.60	$28.60
Purchase #6	$132.48	3.421%	$137.0121	$137.01	$137.00	$137.00
Purchase #7	$174.76	12.620%	$196.8147	$196.81	$196.80	$196.80
7 purchase totals =	$759.53		$822.6464	$822.62	$822.60	$822.60