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	$79.61	12.430%	$89.5055	$89.51	$89.50	$89.50
Purchase #2	$44.73	10.448%	$49.4034	$49.40	$49.40	$49.40
Purchase #3	$104.60	4.386%	$109.1878	$109.19	$109.20	$109.20
Purchase #4	$192.32	3.696%	$199.4281	$199.43	$199.45	$199.40
Purchase #5	$109.77	9.254%	$119.9281	$119.93	$119.95	$119.90
Purchase #6	$168.70	3.127%	$173.9752	$173.98	$174.00	$174.00
Purchase #7	$88.59	6.675%	$94.5034	$94.50	$94.50	$94.50
7 purchase totals =	$788.32		$835.9315	$835.94	$836.00	$835.90