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	$222.66	12.649%	$250.8243	$250.82	$250.80	$250.80
Purchase #2	$162.68	4.113%	$169.371	$169.37	$169.35	$169.40
Purchase #3	$124.28	4.211%	$129.5134	$129.51	$129.50	$129.50
Purchase #4	$106.32	6.738%	$113.4838	$113.48	$113.50	$113.50
Purchase #5	$162.48	5.803%	$171.9087	$171.91	$171.90	$171.90
Purchase #6	$217.49	11.192%	$241.8315	$241.83	$241.85	$241.80
Purchase #7	$12.34	5.392%	$13.0054	$13.01	$13.00	$13.00
7 purchase totals =	$1,008.25		$1,089.9381	$1,089.93	$1,089.90	$1,089.90