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	$244.83	9.673%	$268.5124	$268.51	$268.50	$268.50
Purchase #2	$178.31	12.311%	$200.2617	$200.26	$200.25	$200.30
Purchase #3	$66.65	5.491%	$70.3098	$70.31	$70.30	$70.30
Purchase #4	$71.59	11.817%	$80.0498	$80.05	$80.05	$80.00
Purchase #5	$37.97	8.678%	$41.265	$41.27	$41.25	$41.30
Purchase #6	$198.39	12.827%	$223.8375	$223.84	$223.85	$223.80
Purchase #7	$194.71	7.256%	$208.8382	$208.84	$208.85	$208.80
7 purchase totals =	$992.45		$1,093.0744	$1,093.08	$1,093.05	$1,093.00