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	$110.25	3.102%	$113.67	$113.67	$113.65	$113.70
Purchase #2	$82.67	8.421%	$89.6316	$89.63	$89.65	$89.60
Purchase #3	$66.48	9.194%	$72.5922	$72.59	$72.60	$72.60
Purchase #4	$177.50	11.826%	$198.4912	$198.49	$198.50	$198.50
Purchase #5	$111.73	13.526%	$126.8426	$126.84	$126.85	$126.80
Purchase #6	$68.97	12.777%	$77.7823	$77.78	$77.80	$77.80
Purchase #7	$229.51	5.680%	$242.5462	$242.55	$242.55	$242.50
7 purchase totals =	$847.11		$921.5561	$921.55	$921.60	$921.50