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	$148.31	8.506%	$160.9252	$160.93	$160.95	$160.90
Purchase #2	$60.88	12.338%	$68.3914	$68.39	$68.40	$68.40
Purchase #3	$102.66	6.457%	$109.2888	$109.29	$109.30	$109.30
Purchase #4	$40.25	5.561%	$42.4883	$42.49	$42.50	$42.50
Purchase #5	$144.31	12.676%	$162.6027	$162.60	$162.60	$162.60
Purchase #6	$230.94	12.576%	$259.983	$259.98	$260.00	$260.00
Purchase #7	$131.40	4.133%	$136.8308	$136.83	$136.85	$136.80
7 purchase totals =	$858.75		$940.5102	$940.51	$940.60	$940.50