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	$9.68	10.226%	$10.6699	$10.67	$10.65	$10.70
Purchase #2	$109.89	11.508%	$122.5361	$122.54	$122.55	$122.50
Purchase #3	$34.45	12.691%	$38.822	$38.82	$38.80	$38.80
Purchase #4	$125.56	6.653%	$133.9135	$133.91	$133.90	$133.90
Purchase #5	$144.72	13.334%	$164.017	$164.02	$164.00	$164.00
Purchase #6	$23.39	4.554%	$24.4552	$24.46	$24.45	$24.50
Purchase #7	$87.95	12.597%	$99.0291	$99.03	$99.05	$99.00
7 purchase totals =	$535.64		$593.4428	$593.45	$593.40	$593.40