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	$242.38	10.192%	$267.0834	$267.08	$267.10	$267.10
Purchase #2	$38.27	4.575%	$40.0209	$40.02	$40.00	$40.00
Purchase #3	$177.43	3.801%	$184.1741	$184.17	$184.15	$184.20
Purchase #4	$108.50	4.593%	$113.4834	$113.48	$113.50	$113.50
Purchase #5	$141.32	8.663%	$153.5626	$153.56	$153.55	$153.60
Purchase #6	$91.64	12.678%	$103.2581	$103.26	$103.25	$103.30
Purchase #7	$78.71	4.516%	$82.2645	$82.26	$82.25	$82.30
7 purchase totals =	$878.25		$943.8470	$943.83	$943.80	$944.00