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	$165.51	8.443%	$179.484	$179.48	$179.50	$179.50
Purchase #2	$151.55	8.430%	$164.3257	$164.33	$164.35	$164.30
Purchase #3	$20.35	3.254%	$21.0122	$21.01	$21.00	$21.00
Purchase #4	$69.95	9.267%	$76.4323	$76.43	$76.45	$76.40
Purchase #5	$88.83	3.134%	$91.6139	$91.61	$91.60	$91.60
Purchase #6	$205.92	13.858%	$234.4564	$234.46	$234.45	$234.50
Purchase #7	$142.86	11.163%	$158.8075	$158.81	$158.80	$158.80
7 purchase totals =	$844.97		$926.1320	$926.13	$926.15	$926.10