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	$150.91	13.409%	$171.1455	$171.15	$171.15	$171.10
Purchase #2	$41.47	4.141%	$43.1873	$43.19	$43.20	$43.20
Purchase #3	$188.73	13.248%	$213.733	$213.73	$213.75	$213.70
Purchase #4	$152.83	7.871%	$164.8592	$164.86	$164.85	$164.90
Purchase #5	$73.92	4.510%	$77.2538	$77.25	$77.25	$77.30
Purchase #6	$171.30	12.874%	$193.3532	$193.35	$193.35	$193.40
Purchase #7	$84.72	7.283%	$90.8902	$90.89	$90.90	$90.90
7 purchase totals =	$863.88		$954.4222	$954.42	$954.45	$954.50