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	$52.58	12.356%	$59.0768	$59.08	$59.10	$59.10
Purchase #2	$123.82	12.544%	$139.352	$139.35	$139.35	$139.40
Purchase #3	$43.57	12.146%	$48.862	$48.86	$48.85	$48.90
Purchase #4	$7.99	4.499%	$8.3495	$8.35	$8.35	$8.30
Purchase #5	$82.28	11.807%	$91.9948	$91.99	$92.00	$92.00
Purchase #6	$27.30	8.393%	$29.5913	$29.59	$29.60	$29.60
Purchase #7	$156.78	10.257%	$172.8609	$172.86	$172.85	$172.90
7 purchase totals =	$494.32		$550.0873	$550.08	$550.10	$550.20