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	$16.77	8.210%	$18.1468	$18.15	$18.15	$18.10
Purchase #2	$224.78	3.824%	$233.3756	$233.38	$233.40	$233.40
Purchase #3	$207.80	13.185%	$235.1984	$235.20	$235.20	$235.20
Purchase #4	$100.89	10.799%	$111.7851	$111.79	$111.80	$111.80
Purchase #5	$155.57	10.203%	$171.4428	$171.44	$171.45	$171.40
Purchase #6	$161.30	8.151%	$174.4476	$174.45	$174.45	$174.40
Purchase #7	$100.47	3.352%	$103.8378	$103.84	$103.85	$103.80
7 purchase totals =	$967.58		$1,048.2341	$1,048.25	$1,048.30	$1,048.10