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	$102.82	5.664%	$108.6437	$108.64	$108.65	$108.60
Purchase #2	$181.67	13.838%	$206.8095	$206.81	$206.80	$206.80
Purchase #3	$185.36	12.772%	$209.0342	$209.03	$209.05	$209.00
Purchase #4	$158.33	4.121%	$164.8548	$164.85	$164.85	$164.90
Purchase #5	$9.71	4.472%	$10.1442	$10.14	$10.15	$10.10
Purchase #6	$104.37	6.814%	$111.4818	$111.48	$111.50	$111.50
Purchase #7	$10.47	5.314%	$11.0264	$11.03	$11.05	$11.00
7 purchase totals =	$752.73		$821.9946	$821.98	$822.05	$821.90