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	$105.90	8.436%	$114.8337	$114.83	$114.85	$114.80
Purchase #2	$232.74	5.124%	$244.6656	$244.67	$244.65	$244.70
Purchase #3	$18.38	11.621%	$20.5159	$20.52	$20.50	$20.50
Purchase #4	$204.68	9.280%	$223.6743	$223.67	$223.65	$223.70
Purchase #5	$83.81	10.490%	$92.6017	$92.60	$92.60	$92.60
Purchase #6	$19.90	3.112%	$20.5193	$20.52	$20.50	$20.50
Purchase #7	$100.61	4.364%	$105.0006	$105.00	$105.00	$105.00
7 purchase totals =	$766.02		$821.8111	$821.81	$821.75	$821.80