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	$242.61	11.744%	$271.1021	$271.10	$271.10	$271.10
Purchase #2	$58.86	13.308%	$66.6931	$66.69	$66.70	$66.70
Purchase #3	$134.28	8.469%	$145.6522	$145.65	$145.65	$145.70
Purchase #4	$149.44	6.211%	$158.7217	$158.72	$158.70	$158.70
Purchase #5	$179.85	9.249%	$196.4843	$196.48	$196.50	$196.50
Purchase #6	$78.79	10.689%	$87.2119	$87.21	$87.20	$87.20
Purchase #7	$80.53	11.540%	$89.8232	$89.82	$89.80	$89.80
7 purchase totals =	$924.36		$1,015.6885	$1,015.67	$1,015.65	$1,015.70