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	$51.46	9.127%	$56.1568	$56.16	$56.15	$56.20
Purchase #2	$19.85	5.754%	$20.9922	$20.99	$21.00	$21.00
Purchase #3	$85.94	11.601%	$95.9099	$95.91	$95.90	$95.90
Purchase #4	$220.81	5.736%	$233.4757	$233.48	$233.50	$233.50
Purchase #5	$28.70	3.693%	$29.7599	$29.76	$29.75	$29.80
Purchase #6	$163.91	5.321%	$172.6317	$172.63	$172.65	$172.60
Purchase #7	$159.87	7.865%	$172.4438	$172.44	$172.45	$172.40
7 purchase totals =	$730.54		$781.3700	$781.37	$781.40	$781.40