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	$79.25	8.342%	$85.861	$85.86	$85.85	$85.90
Purchase #2	$112.81	9.541%	$123.5732	$123.57	$123.55	$123.60
Purchase #3	$117.74	13.378%	$133.4913	$133.49	$133.50	$133.50
Purchase #4	$174.64	8.139%	$188.8539	$188.85	$188.85	$188.90
Purchase #5	$17.49	5.528%	$18.4568	$18.46	$18.45	$18.50
Purchase #6	$147.54	5.176%	$155.1767	$155.18	$155.20	$155.20
Purchase #7	$104.46	9.634%	$114.5237	$114.52	$114.50	$114.50
7 purchase totals =	$753.93		$819.9366	$819.93	$819.90	$820.10