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	$63.43	4.718%	$66.4226	$66.42	$66.40	$66.40
Purchase #2	$185.31	5.359%	$195.2408	$195.24	$195.25	$195.20
Purchase #3	$78.51	6.796%	$83.8455	$83.85	$83.85	$83.80
Purchase #4	$176.57	13.533%	$200.4652	$200.47	$200.45	$200.50
Purchase #5	$102.89	10.759%	$113.9599	$113.96	$113.95	$114.00
Purchase #6	$119.52	12.609%	$134.5903	$134.59	$134.60	$134.60
Purchase #7	$148.73	6.766%	$158.7931	$158.79	$158.80	$158.80
7 purchase totals =	$874.96		$953.3174	$953.32	$953.30	$953.30