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	$141.82	5.155%	$149.1308	$149.13	$149.15	$149.10
Purchase #2	$220.74	3.659%	$228.8169	$228.82	$228.80	$228.80
Purchase #3	$86.73	4.763%	$90.8609	$90.86	$90.85	$90.90
Purchase #4	$134.38	3.516%	$139.1048	$139.10	$139.10	$139.10
Purchase #5	$66.83	10.137%	$73.6046	$73.60	$73.60	$73.60
Purchase #6	$116.90	13.332%	$132.4851	$132.49	$132.50	$132.50
Purchase #7	$177.35	8.215%	$191.9193	$191.92	$191.90	$191.90
7 purchase totals =	$944.75		$1,005.9224	$1,005.92	$1,005.90	$1,005.90