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	$81.51	5.311%	$85.839	$85.84	$85.85	$85.80
Purchase #2	$117.38	13.709%	$133.4716	$133.47	$133.45	$133.50
Purchase #3	$109.90	8.372%	$119.1008	$119.10	$119.10	$119.10
Purchase #4	$124.93	7.387%	$134.1586	$134.16	$134.15	$134.20
Purchase #5	$37.53	11.411%	$41.8125	$41.81	$41.80	$41.80
Purchase #6	$244.30	11.293%	$271.8888	$271.89	$271.90	$271.90
Purchase #7	$51.27	7.631%	$55.1824	$55.18	$55.20	$55.20
7 purchase totals =	$766.82		$841.4537	$841.45	$841.45	$841.50