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	$230.57	10.108%	$253.876	$253.88	$253.90	$253.90
Purchase #2	$213.38	5.319%	$224.7297	$224.73	$224.75	$224.70
Purchase #3	$34.94	11.248%	$38.8701	$38.87	$38.85	$38.90
Purchase #4	$141.56	6.664%	$150.9936	$150.99	$151.00	$151.00
Purchase #5	$148.34	7.146%	$158.9404	$158.94	$158.95	$158.90
Purchase #6	$122.98	12.364%	$138.1852	$138.19	$138.20	$138.20
Purchase #7	$12.46	3.569%	$12.9047	$12.90	$12.90	$12.90
7 purchase totals =	$904.23		$978.4997	$978.50	$978.55	$978.50