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	$60.53	9.453%	$66.2519	$66.25	$66.25	$66.30
Purchase #2	$92.32	11.578%	$103.0088	$103.01	$103.00	$103.00
Purchase #3	$21.75	10.235%	$23.9761	$23.98	$24.00	$24.00
Purchase #4	$103.42	8.839%	$112.5613	$112.56	$112.55	$112.60
Purchase #5	$57.86	5.618%	$61.1106	$61.11	$61.10	$61.10
Purchase #6	$36.78	4.339%	$38.3759	$38.38	$38.40	$38.40
Purchase #7	$139.55	3.127%	$143.9137	$143.91	$143.90	$143.90
7 purchase totals =	$512.21		$549.1983	$549.20	$549.20	$549.30