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	$83.28	13.462%	$94.4912	$94.49	$94.50	$94.50
Purchase #2	$113.48	8.689%	$123.3403	$123.34	$123.35	$123.30
Purchase #3	$62.38	10.483%	$68.9193	$68.92	$68.90	$68.90
Purchase #4	$171.62	6.105%	$182.0974	$182.10	$182.10	$182.10
Purchase #5	$164.71	10.154%	$181.4347	$181.43	$181.45	$181.40
Purchase #6	$133.27	12.563%	$150.0127	$150.01	$150.00	$150.00
Purchase #7	$161.86	9.251%	$176.8337	$176.83	$176.85	$176.80
7 purchase totals =	$890.60		$977.1293	$977.12	$977.15	$977.00