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	$42.70	12.412%	$47.9999	$48.00	$48.00	$48.00
Purchase #2	$88.86	13.201%	$100.5904	$100.59	$100.60	$100.60
Purchase #3	$88.42	8.218%	$95.6864	$95.69	$95.70	$95.70
Purchase #4	$58.83	13.414%	$66.7215	$66.72	$66.70	$66.70
Purchase #5	$231.45	3.609%	$239.803	$239.80	$239.80	$239.80
Purchase #6	$119.26	3.651%	$123.6142	$123.61	$123.60	$123.60
Purchase #7	$205.64	6.313%	$218.6221	$218.62	$218.60	$218.60
7 purchase totals =	$835.16		$893.0375	$893.03	$893.00	$893.00