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	$134.28	13.728%	$152.714	$152.71	$152.70	$152.70
Purchase #2	$27.33	8.105%	$29.5451	$29.55	$29.55	$29.50
Purchase #3	$162.32	11.367%	$180.7709	$180.77	$180.75	$180.80
Purchase #4	$83.60	7.788%	$90.1108	$90.11	$90.10	$90.10
Purchase #5	$75.55	6.681%	$80.5975	$80.60	$80.60	$80.60
Purchase #6	$100.40	7.578%	$108.0083	$108.01	$108.00	$108.00
Purchase #7	$163.46	10.324%	$180.3356	$180.34	$180.35	$180.30
7 purchase totals =	$746.94		$822.0822	$822.09	$822.05	$822.00