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	$151.27	12.309%	$169.8898	$169.89	$169.90	$169.90
Purchase #2	$64.58	4.576%	$67.5352	$67.54	$67.55	$67.50
Purchase #3	$84.90	5.142%	$89.2656	$89.27	$89.25	$89.30
Purchase #4	$83.71	11.245%	$93.1232	$93.12	$93.10	$93.10
Purchase #5	$9.49	5.650%	$10.0262	$10.03	$10.05	$10.00
Purchase #6	$91.44	12.188%	$102.5847	$102.58	$102.60	$102.60
Purchase #7	$24.64	10.775%	$27.295	$27.30	$27.30	$27.30
7 purchase totals =	$510.03		$559.7197	$559.73	$559.75	$559.70