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	$125.89	8.514%	$136.6083	$136.61	$136.60	$136.60
Purchase #2	$157.25	4.624%	$164.5212	$164.52	$164.50	$164.50
Purchase #3	$55.68	3.506%	$57.6321	$57.63	$57.65	$57.60
Purchase #4	$106.57	4.608%	$111.4807	$111.48	$111.50	$111.50
Purchase #5	$23.62	4.240%	$24.6215	$24.62	$24.60	$24.60
Purchase #6	$155.66	10.357%	$171.7817	$171.78	$171.80	$171.80
Purchase #7	$197.85	8.591%	$214.8473	$214.85	$214.85	$214.80
7 purchase totals =	$822.52		$881.4928	$881.49	$881.50	$881.40