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	$109.81	5.791%	$116.1691	$116.17	$116.15	$116.20
Purchase #2	$123.59	4.140%	$128.7066	$128.71	$128.70	$128.70
Purchase #3	$217.75	12.716%	$245.4391	$245.44	$245.45	$245.40
Purchase #4	$216.44	10.671%	$239.5363	$239.54	$239.55	$239.50
Purchase #5	$208.72	4.696%	$218.5215	$218.52	$218.50	$218.50
Purchase #6	$35.96	7.377%	$38.6128	$38.61	$38.60	$38.60
Purchase #7	$85.83	12.823%	$96.836	$96.84	$96.85	$96.80
7 purchase totals =	$998.10		$1,083.8214	$1,083.83	$1,083.80	$1,083.70