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	$100.61	8.348%	$109.0089	$109.01	$109.00	$109.00
Purchase #2	$128.40	12.282%	$144.1701	$144.17	$144.15	$144.20
Purchase #3	$34.52	8.238%	$37.3638	$37.36	$37.35	$37.40
Purchase #4	$242.83	5.114%	$255.2483	$255.25	$255.25	$255.20
Purchase #5	$64.94	5.416%	$68.4572	$68.46	$68.45	$68.50
Purchase #6	$24.93	11.588%	$27.8189	$27.82	$27.80	$27.80
Purchase #7	$50.59	12.682%	$57.0058	$57.01	$57.00	$57.00
7 purchase totals =	$646.82		$699.0730	$699.08	$699.00	$699.10