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	$42.38	6.545%	$45.1538	$45.15	$45.15	$45.20
Purchase #2	$28.83	10.772%	$31.9356	$31.94	$31.95	$31.90
Purchase #3	$191.95	9.861%	$210.8782	$210.88	$210.90	$210.90
Purchase #4	$82.80	4.580%	$86.5922	$86.59	$86.60	$86.60
Purchase #5	$42.66	12.461%	$47.9759	$47.98	$48.00	$48.00
Purchase #6	$38.67	3.752%	$40.1209	$40.12	$40.10	$40.10
Purchase #7	$99.91	4.213%	$104.1192	$104.12	$104.10	$104.10
7 purchase totals =	$527.20		$566.7758	$566.78	$566.80	$566.80