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	$15.94	13.126%	$18.0323	$18.03	$18.05	$18.00
Purchase #2	$213.43	8.576%	$231.7338	$231.73	$231.75	$231.70
Purchase #3	$151.57	5.874%	$160.4732	$160.47	$160.45	$160.50
Purchase #4	$67.35	4.612%	$70.4562	$70.46	$70.45	$70.50
Purchase #5	$85.34	4.723%	$89.3706	$89.37	$89.35	$89.40
Purchase #6	$86.70	13.116%	$98.0716	$98.07	$98.05	$98.10
Purchase #7	$207.61	11.340%	$231.153	$231.15	$231.15	$231.20
7 purchase totals =	$827.94		$899.2907	$899.28	$899.25	$899.40