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	$102.89	9.680%	$112.8498	$112.85	$112.85	$112.80
Purchase #2	$91.71	5.220%	$96.4973	$96.50	$96.50	$96.50
Purchase #3	$171.79	5.157%	$180.6492	$180.65	$180.65	$180.60
Purchase #4	$232.30	4.547%	$242.8627	$242.86	$242.85	$242.90
Purchase #5	$97.89	13.546%	$111.1502	$111.15	$111.15	$111.20
Purchase #6	$82.57	9.706%	$90.5842	$90.58	$90.60	$90.60
Purchase #7	$35.65	12.147%	$39.9804	$39.98	$40.00	$40.00
7 purchase totals =	$814.80		$874.5738	$874.57	$874.60	$874.60