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	$233.78	13.782%	$265.9996	$266.00	$266.00	$266.00
Purchase #2	$155.33	6.563%	$165.5243	$165.52	$165.50	$165.50
Purchase #3	$152.78	10.196%	$168.3574	$168.36	$168.35	$168.40
Purchase #4	$144.84	9.148%	$158.09	$158.09	$158.10	$158.10
Purchase #5	$119.83	13.121%	$135.5529	$135.55	$135.55	$135.60
Purchase #6	$153.89	13.561%	$174.759	$174.76	$174.75	$174.80
Purchase #7	$159.90	5.439%	$168.597	$168.60	$168.60	$168.60
7 purchase totals =	$1,120.35		$1,236.8802	$1,236.88	$1,236.85	$1,237.00