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	$125.87	11.103%	$139.8453	$139.85	$139.85	$139.80
Purchase #2	$158.83	5.440%	$167.4704	$167.47	$167.45	$167.50
Purchase #3	$37.79	7.106%	$40.4754	$40.48	$40.50	$40.50
Purchase #4	$60.27	9.457%	$65.9697	$65.97	$65.95	$66.00
Purchase #5	$211.74	5.625%	$223.6504	$223.65	$223.65	$223.70
Purchase #6	$13.93	7.284%	$14.9447	$14.94	$14.95	$14.90
Purchase #7	$119.91	6.166%	$127.3037	$127.30	$127.30	$127.30
7 purchase totals =	$728.34		$779.6596	$779.66	$779.65	$779.70