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	$238.54	12.597%	$268.5889	$268.59	$268.60	$268.60
Purchase #2	$81.64	8.369%	$88.4725	$88.47	$88.45	$88.50
Purchase #3	$192.32	3.725%	$199.4839	$199.48	$199.50	$199.50
Purchase #4	$30.88	9.691%	$33.8726	$33.87	$33.85	$33.90
Purchase #5	$82.83	13.651%	$94.1371	$94.14	$94.15	$94.10
Purchase #6	$243.36	6.697%	$259.6578	$259.66	$259.65	$259.70
Purchase #7	$200.85	13.814%	$228.5954	$228.60	$228.60	$228.60
7 purchase totals =	$1,070.42		$1,172.8082	$1,172.81	$1,172.80	$1,172.90