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	$246.59	5.773%	$260.8256	$260.83	$260.85	$260.80
Purchase #2	$108.85	6.573%	$116.0047	$116.00	$116.00	$116.00
Purchase #3	$79.80	6.684%	$85.1338	$85.13	$85.15	$85.10
Purchase #4	$73.44	6.810%	$78.4413	$78.44	$78.45	$78.40
Purchase #5	$118.37	12.796%	$133.5166	$133.52	$133.50	$133.50
Purchase #6	$63.63	13.175%	$72.0133	$72.01	$72.00	$72.00
Purchase #7	$19.40	4.240%	$20.2226	$20.22	$20.20	$20.20
7 purchase totals =	$710.08		$766.1579	$766.15	$766.15	$766.00