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	$23.60	9.723%	$25.8946	$25.89	$25.90	$25.90
Purchase #2	$149.80	11.839%	$167.5348	$167.53	$167.55	$167.50
Purchase #3	$230.77	10.276%	$254.4839	$254.48	$254.50	$254.50
Purchase #4	$85.80	4.169%	$89.377	$89.38	$89.40	$89.40
Purchase #5	$37.68	7.577%	$40.535	$40.54	$40.55	$40.50
Purchase #6	$68.47	5.853%	$72.4775	$72.48	$72.50	$72.50
Purchase #7	$13.33	11.872%	$14.9125	$14.91	$14.90	$14.90
7 purchase totals =	$609.45		$665.2153	$665.21	$665.30	$665.20