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	$178.78	5.739%	$189.0402	$189.04	$189.05	$189.00
Purchase #2	$152.60	10.256%	$168.2507	$168.25	$168.25	$168.30
Purchase #3	$164.74	7.122%	$176.4728	$176.47	$176.45	$176.50
Purchase #4	$214.74	5.204%	$225.9151	$225.92	$225.90	$225.90
Purchase #5	$91.41	13.673%	$103.9085	$103.91	$103.90	$103.90
Purchase #6	$86.34	3.291%	$89.1814	$89.18	$89.20	$89.20
Purchase #7	$150.94	4.269%	$157.3836	$157.38	$157.40	$157.40
7 purchase totals =	$1,039.55		$1,110.1523	$1,110.15	$1,110.15	$1,110.20