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	$99.53	8.803%	$108.2916	$108.29	$108.30	$108.30
Purchase #2	$29.95	3.785%	$31.0836	$31.08	$31.10	$31.10
Purchase #3	$219.87	12.140%	$246.5622	$246.56	$246.55	$246.60
Purchase #4	$221.61	12.632%	$249.6038	$249.60	$249.60	$249.60
Purchase #5	$29.88	13.535%	$33.9243	$33.92	$33.90	$33.90
Purchase #6	$105.77	7.382%	$113.5779	$113.58	$113.60	$113.60
Purchase #7	$60.54	11.573%	$67.5463	$67.55	$67.55	$67.50
7 purchase totals =	$767.15		$850.5897	$850.58	$850.60	$850.60