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	$17.50	11.574%	$19.5255	$19.53	$19.55	$19.50
Purchase #2	$30.31	6.840%	$32.3832	$32.38	$32.40	$32.40
Purchase #3	$155.48	10.691%	$172.1024	$172.10	$172.10	$172.10
Purchase #4	$228.53	5.625%	$241.3848	$241.38	$241.40	$241.40
Purchase #5	$34.29	6.733%	$36.5987	$36.60	$36.60	$36.60
Purchase #6	$90.98	5.575%	$96.0521	$96.05	$96.05	$96.10
Purchase #7	$227.32	3.181%	$234.551	$234.55	$234.55	$234.60
7 purchase totals =	$784.41		$832.5977	$832.59	$832.65	$832.70