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	$189.93	8.154%	$205.4169	$205.42	$205.40	$205.40
Purchase #2	$132.25	5.800%	$139.9205	$139.92	$139.90	$139.90
Purchase #3	$137.36	12.768%	$154.8981	$154.90	$154.90	$154.90
Purchase #4	$29.32	12.554%	$33.0008	$33.00	$33.00	$33.00
Purchase #5	$20.29	10.154%	$22.3502	$22.35	$22.35	$22.40
Purchase #6	$86.38	3.129%	$89.0828	$89.08	$89.10	$89.10
Purchase #7	$123.80	10.852%	$137.2348	$137.23	$137.25	$137.20
7 purchase totals =	$719.33		$781.9041	$781.90	$781.90	$781.90