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	$94.82	9.402%	$103.735	$103.74	$103.75	$103.70
Purchase #2	$86.47	4.653%	$90.4934	$90.49	$90.50	$90.50
Purchase #3	$131.35	4.742%	$137.5786	$137.58	$137.60	$137.60
Purchase #4	$11.45	11.169%	$12.7289	$12.73	$12.75	$12.70
Purchase #5	$179.40	6.857%	$191.7015	$191.70	$191.70	$191.70
Purchase #6	$118.46	10.461%	$130.8521	$130.85	$130.85	$130.90
Purchase #7	$174.99	9.665%	$191.9028	$191.90	$191.90	$191.90
7 purchase totals =	$796.94		$858.9923	$858.99	$859.05	$859.00