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	$19.69	5.841%	$20.8401	$20.84	$20.85	$20.80
Purchase #2	$186.30	10.337%	$205.5578	$205.56	$205.55	$205.60
Purchase #3	$63.28	13.297%	$71.6943	$71.69	$71.70	$71.70
Purchase #4	$137.85	5.856%	$145.9225	$145.92	$145.90	$145.90
Purchase #5	$144.59	6.428%	$153.8842	$153.88	$153.90	$153.90
Purchase #6	$46.53	8.190%	$50.3408	$50.34	$50.35	$50.30
Purchase #7	$194.88	11.659%	$217.6011	$217.60	$217.60	$217.60
7 purchase totals =	$793.12		$865.8408	$865.83	$865.85	$865.80