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	$13.48	13.466%	$15.2952	$15.30	$15.30	$15.30
Purchase #2	$160.84	11.630%	$179.5457	$179.55	$179.55	$179.50
Purchase #3	$6.48	13.553%	$7.3582	$7.36	$7.35	$7.40
Purchase #4	$162.75	5.356%	$171.4669	$171.47	$171.45	$171.50
Purchase #5	$127.37	4.732%	$133.3971	$133.40	$133.40	$133.40
Purchase #6	$56.78	11.861%	$63.5147	$63.51	$63.50	$63.50
Purchase #7	$85.94	12.860%	$96.9919	$96.99	$97.00	$97.00
7 purchase totals =	$613.64		$667.5697	$667.58	$667.55	$667.60