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	$179.32	6.274%	$190.5705	$190.57	$190.55	$190.60
Purchase #2	$121.32	12.589%	$136.593	$136.59	$136.60	$136.60
Purchase #3	$210.90	10.242%	$232.5004	$232.50	$232.50	$232.50
Purchase #4	$187.99	4.739%	$196.8988	$196.90	$196.90	$196.90
Purchase #5	$178.43	5.126%	$187.5763	$187.58	$187.60	$187.60
Purchase #6	$30.40	8.243%	$32.9059	$32.91	$32.90	$32.90
Purchase #7	$162.54	7.682%	$175.0263	$175.03	$175.05	$175.00
7 purchase totals =	$1,070.90		$1,152.0712	$1,152.08	$1,152.10	$1,152.10