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	$246.55	9.327%	$269.5457	$269.55	$269.55	$269.50
Purchase #2	$40.51	10.491%	$44.7599	$44.76	$44.75	$44.80
Purchase #3	$95.33	5.712%	$100.7752	$100.78	$100.80	$100.80
Purchase #4	$154.60	7.596%	$166.3434	$166.34	$166.35	$166.30
Purchase #5	$74.61	8.764%	$81.1488	$81.15	$81.15	$81.10
Purchase #6	$27.94	3.296%	$28.8609	$28.86	$28.85	$28.90
Purchase #7	$131.36	7.414%	$141.099	$141.10	$141.10	$141.10
7 purchase totals =	$770.90		$832.5329	$832.54	$832.55	$832.50