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	$128.83	11.776%	$144.001	$144.00	$144.00	$144.00
Purchase #2	$55.40	4.714%	$58.0116	$58.01	$58.00	$58.00
Purchase #3	$55.32	6.833%	$59.1	$59.10	$59.10	$59.10
Purchase #4	$143.31	10.188%	$157.9104	$157.91	$157.90	$157.90
Purchase #5	$58.76	12.234%	$65.9487	$65.95	$65.95	$65.90
Purchase #6	$46.63	5.631%	$49.2557	$49.26	$49.25	$49.30
Purchase #7	$37.78	6.480%	$40.2281	$40.23	$40.25	$40.20
7 purchase totals =	$526.03		$574.4555	$574.46	$574.45	$574.40