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	$5.71	3.207%	$5.8931	$5.89	$5.90	$5.90
Purchase #2	$10.46	8.197%	$11.3174	$11.32	$11.30	$11.30
Purchase #3	$83.86	13.779%	$95.4151	$95.42	$95.40	$95.40
Purchase #4	$85.38	5.521%	$90.0938	$90.09	$90.10	$90.10
Purchase #5	$34.29	7.484%	$36.8563	$36.86	$36.85	$36.90
Purchase #6	$223.38	13.665%	$253.9049	$253.90	$253.90	$253.90
Purchase #7	$15.30	3.747%	$15.8733	$15.87	$15.85	$15.90
7 purchase totals =	$458.38		$509.3539	$509.35	$509.30	$509.40