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	$157.45	13.833%	$179.2301	$179.23	$179.25	$179.20
Purchase #2	$37.83	9.840%	$41.5525	$41.55	$41.55	$41.60
Purchase #3	$165.57	8.479%	$179.6087	$179.61	$179.60	$179.60
Purchase #4	$148.71	9.349%	$162.6129	$162.61	$162.60	$162.60
Purchase #5	$230.47	8.348%	$249.7096	$249.71	$249.70	$249.70
Purchase #6	$127.66	12.475%	$143.5856	$143.59	$143.60	$143.60
Purchase #7	$38.34	13.494%	$43.5136	$43.51	$43.50	$43.50
7 purchase totals =	$906.03		$999.8130	$999.81	$999.80	$999.80