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	$28.70	13.610%	$32.6061	$32.61	$32.60	$32.60
Purchase #2	$123.91	12.313%	$139.167	$139.17	$139.15	$139.20
Purchase #3	$89.69	9.311%	$98.041	$98.04	$98.05	$98.00
Purchase #4	$136.60	5.373%	$143.9395	$143.94	$143.95	$143.90
Purchase #5	$151.49	13.387%	$171.77	$171.77	$171.75	$171.80
Purchase #6	$73.34	5.710%	$77.5277	$77.53	$77.55	$77.50
Purchase #7	$48.42	9.303%	$52.9245	$52.92	$52.90	$52.90
7 purchase totals =	$652.15		$715.9758	$715.98	$715.95	$715.90