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	$26.96	11.206%	$29.9811	$29.98	$30.00	$30.00
Purchase #2	$56.25	5.379%	$59.2757	$59.28	$59.30	$59.30
Purchase #3	$32.82	4.379%	$34.2572	$34.26	$34.25	$34.30
Purchase #4	$51.57	7.564%	$55.4708	$55.47	$55.45	$55.50
Purchase #5	$213.70	5.317%	$225.0624	$225.06	$225.05	$225.10
Purchase #6	$107.55	4.143%	$112.0058	$112.01	$112.00	$112.00
Purchase #7	$21.42	6.842%	$22.8856	$22.89	$22.90	$22.90
7 purchase totals =	$510.27		$538.9386	$538.95	$538.95	$539.10