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	$240.32	13.388%	$272.494	$272.49	$272.50	$272.50
Purchase #2	$238.47	12.323%	$267.8567	$267.86	$267.85	$267.90
Purchase #3	$214.92	12.418%	$241.6088	$241.61	$241.60	$241.60
Purchase #4	$82.77	7.510%	$88.986	$88.99	$89.00	$89.00
Purchase #5	$207.95	11.427%	$231.7124	$231.71	$231.70	$231.70
Purchase #6	$84.55	5.115%	$88.8747	$88.87	$88.85	$88.90
Purchase #7	$99.73	9.702%	$109.4058	$109.41	$109.40	$109.40
7 purchase totals =	$1,168.71		$1,300.9384	$1,300.94	$1,300.90	$1,301.00