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	$157.38	7.129%	$168.5996	$168.60	$168.60	$168.60
Purchase #2	$134.43	11.609%	$150.036	$150.04	$150.05	$150.00
Purchase #3	$214.28	6.630%	$228.4868	$228.49	$228.50	$228.50
Purchase #4	$92.65	8.814%	$100.8162	$100.82	$100.80	$100.80
Purchase #5	$105.83	11.262%	$117.7486	$117.75	$117.75	$117.70
Purchase #6	$112.91	6.540%	$120.2943	$120.29	$120.30	$120.30
Purchase #7	$42.33	4.706%	$44.322	$44.32	$44.30	$44.30
7 purchase totals =	$859.81		$930.3035	$930.31	$930.30	$930.20