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	$16.75	10.294%	$18.4742	$18.47	$18.45	$18.50
Purchase #2	$106.69	4.173%	$111.1422	$111.14	$111.15	$111.10
Purchase #3	$106.34	5.752%	$112.4567	$112.46	$112.45	$112.50
Purchase #4	$120.80	9.819%	$132.6614	$132.66	$132.65	$132.70
Purchase #5	$40.30	4.166%	$41.9789	$41.98	$42.00	$42.00
Purchase #6	$52.31	9.202%	$57.1236	$57.12	$57.10	$57.10
Purchase #7	$206.58	6.467%	$219.9395	$219.94	$219.95	$219.90
7 purchase totals =	$649.77		$693.7765	$693.77	$693.75	$693.80