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	$115.32	13.558%	$130.9551	$130.96	$130.95	$131.00
Purchase #2	$81.64	10.832%	$90.4832	$90.48	$90.50	$90.50
Purchase #3	$161.31	13.224%	$182.6416	$182.64	$182.65	$182.60
Purchase #4	$160.35	8.534%	$174.0343	$174.03	$174.05	$174.00
Purchase #5	$100.51	8.795%	$109.3499	$109.35	$109.35	$109.30
Purchase #6	$166.80	4.223%	$173.844	$173.84	$173.85	$173.80
Purchase #7	$92.89	13.854%	$105.759	$105.76	$105.75	$105.80
7 purchase totals =	$878.82		$967.0671	$967.06	$967.10	$967.00