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	$78.29	3.678%	$81.1695	$81.17	$81.15	$81.20
Purchase #2	$105.64	8.354%	$114.4652	$114.47	$114.45	$114.50
Purchase #3	$228.53	5.823%	$241.8373	$241.84	$241.85	$241.80
Purchase #4	$109.30	11.438%	$121.8017	$121.80	$121.80	$121.80
Purchase #5	$35.78	8.604%	$38.8585	$38.86	$38.85	$38.90
Purchase #6	$80.72	10.822%	$89.4555	$89.46	$89.45	$89.50
Purchase #7	$162.32	6.780%	$173.3253	$173.33	$173.35	$173.30
7 purchase totals =	$800.58		$860.9130	$860.93	$860.90	$861.00