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	$226.82	10.257%	$250.0849	$250.08	$250.10	$250.10
Purchase #2	$214.39	8.833%	$233.3271	$233.33	$233.35	$233.30
Purchase #3	$142.37	13.309%	$161.318	$161.32	$161.30	$161.30
Purchase #4	$106.54	4.474%	$111.3066	$111.31	$111.30	$111.30
Purchase #5	$217.78	13.665%	$247.5396	$247.54	$247.55	$247.50
Purchase #6	$200.41	5.713%	$211.8594	$211.86	$211.85	$211.90
Purchase #7	$68.84	4.254%	$71.7685	$71.77	$71.75	$71.80
7 purchase totals =	$1,177.15		$1,287.2041	$1,287.21	$1,287.20	$1,287.20