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	$143.85	10.641%	$159.1571	$159.16	$159.15	$159.20
Purchase #2	$207.98	11.235%	$231.3466	$231.35	$231.35	$231.30
Purchase #3	$28.38	12.356%	$31.8866	$31.89	$31.90	$31.90
Purchase #4	$148.62	3.295%	$153.517	$153.52	$153.50	$153.50
Purchase #5	$59.73	10.556%	$66.0351	$66.04	$66.05	$66.00
Purchase #6	$187.86	12.786%	$211.8798	$211.88	$211.90	$211.90
Purchase #7	$130.38	10.562%	$144.1507	$144.15	$144.15	$144.20
7 purchase totals =	$906.80		$997.9729	$997.99	$998.00	$998.00