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	$87.58	5.139%	$92.0807	$92.08	$92.10	$92.10
Purchase #2	$85.89	10.426%	$94.8449	$94.84	$94.85	$94.80
Purchase #3	$79.93	11.509%	$89.1291	$89.13	$89.15	$89.10
Purchase #4	$165.68	5.364%	$174.5671	$174.57	$174.55	$174.60
Purchase #5	$35.95	13.624%	$40.8478	$40.85	$40.85	$40.80
Purchase #6	$73.63	6.483%	$78.4034	$78.40	$78.40	$78.40
Purchase #7	$103.26	7.637%	$111.146	$111.15	$111.15	$111.10
7 purchase totals =	$631.92		$681.0190	$681.02	$681.05	$680.90