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	$83.47	11.202%	$92.8203	$92.82	$92.80	$92.80
Purchase #2	$120.91	13.126%	$136.7806	$136.78	$136.80	$136.80
Purchase #3	$58.55	4.447%	$61.1537	$61.15	$61.15	$61.20
Purchase #4	$69.92	3.462%	$72.3406	$72.34	$72.35	$72.30
Purchase #5	$45.32	12.637%	$51.0471	$51.05	$51.05	$51.00
Purchase #6	$80.96	6.523%	$86.241	$86.24	$86.25	$86.20
Purchase #7	$157.79	4.472%	$164.8464	$164.85	$164.85	$164.80
7 purchase totals =	$616.92		$665.2297	$665.23	$665.25	$665.10