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	$107.70	8.221%	$116.554	$116.55	$116.55	$116.60
Purchase #2	$216.54	4.188%	$225.6087	$225.61	$225.60	$225.60
Purchase #3	$38.79	5.140%	$40.7838	$40.78	$40.80	$40.80
Purchase #4	$88.72	7.208%	$95.1149	$95.11	$95.10	$95.10
Purchase #5	$79.42	8.761%	$86.378	$86.38	$86.40	$86.40
Purchase #6	$165.39	4.798%	$173.3254	$173.33	$173.35	$173.30
Purchase #7	$49.83	13.270%	$56.4424	$56.44	$56.45	$56.40
7 purchase totals =	$746.39		$794.2072	$794.20	$794.25	$794.20