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	$204.90	5.742%	$216.6654	$216.67	$216.65	$216.70
Purchase #2	$141.25	8.336%	$153.0246	$153.02	$153.00	$153.00
Purchase #3	$102.68	5.579%	$108.4085	$108.41	$108.40	$108.40
Purchase #4	$100.80	11.510%	$112.4021	$112.40	$112.40	$112.40
Purchase #5	$227.71	6.495%	$242.4998	$242.50	$242.50	$242.50
Purchase #6	$41.96	9.187%	$45.8149	$45.81	$45.80	$45.80
Purchase #7	$95.73	3.822%	$99.3888	$99.39	$99.40	$99.40
7 purchase totals =	$915.03		$978.2041	$978.20	$978.15	$978.20