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	$24.69	3.133%	$25.4635	$25.46	$25.45	$25.50
Purchase #2	$109.32	3.509%	$113.156	$113.16	$113.15	$113.20
Purchase #3	$69.49	4.416%	$72.5587	$72.56	$72.55	$72.60
Purchase #4	$236.41	5.154%	$248.5946	$248.59	$248.60	$248.60
Purchase #5	$31.42	13.137%	$35.5476	$35.55	$35.55	$35.50
Purchase #6	$7.38	4.339%	$7.7002	$7.70	$7.70	$7.70
Purchase #7	$60.88	12.151%	$68.2775	$68.28	$68.30	$68.30
7 purchase totals =	$539.59		$571.2981	$571.30	$571.30	$571.40