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	$36.34	10.729%	$40.2389	$40.24	$40.25	$40.20
Purchase #2	$172.84	10.155%	$190.3919	$190.39	$190.40	$190.40
Purchase #3	$212.97	13.569%	$241.8679	$241.87	$241.85	$241.90
Purchase #4	$140.33	11.109%	$155.9193	$155.92	$155.90	$155.90
Purchase #5	$95.48	6.269%	$101.4656	$101.47	$101.45	$101.50
Purchase #6	$10.42	10.758%	$11.541	$11.54	$11.55	$11.50
Purchase #7	$71.47	7.215%	$76.6266	$76.63	$76.65	$76.60
7 purchase totals =	$739.85		$818.0512	$818.06	$818.05	$818.00