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	$32.53	11.427%	$36.2472	$36.25	$36.25	$36.20
Purchase #2	$75.96	7.576%	$81.7147	$81.71	$81.70	$81.70
Purchase #3	$207.90	7.194%	$222.8563	$222.86	$222.85	$222.90
Purchase #4	$49.30	13.660%	$56.0344	$56.03	$56.05	$56.00
Purchase #5	$19.49	7.278%	$20.9085	$20.91	$20.90	$20.90
Purchase #6	$211.82	5.666%	$223.8217	$223.82	$223.80	$223.80
Purchase #7	$25.39	11.786%	$28.3825	$28.38	$28.40	$28.40
7 purchase totals =	$622.39		$669.9653	$669.96	$669.95	$669.90