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	$71.51	12.710%	$80.5989	$80.60	$80.60	$80.60
Purchase #2	$92.98	7.580%	$100.0279	$100.03	$100.05	$100.00
Purchase #3	$186.67	5.305%	$196.5728	$196.57	$196.55	$196.60
Purchase #4	$166.96	5.632%	$176.3632	$176.36	$176.35	$176.40
Purchase #5	$243.30	5.561%	$256.8299	$256.83	$256.85	$256.80
Purchase #6	$39.39	3.596%	$40.8065	$40.81	$40.80	$40.80
Purchase #7	$29.93	10.712%	$33.1361	$33.14	$33.15	$33.10
7 purchase totals =	$830.74		$884.3353	$884.34	$884.35	$884.30