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	$125.92	13.200%	$142.5414	$142.54	$142.55	$142.50
Purchase #2	$248.70	7.738%	$267.9444	$267.94	$267.95	$267.90
Purchase #3	$166.27	5.837%	$175.9752	$175.98	$176.00	$176.00
Purchase #4	$236.91	13.236%	$268.2674	$268.27	$268.25	$268.30
Purchase #5	$174.65	4.171%	$181.9347	$181.93	$181.95	$181.90
Purchase #6	$55.99	12.228%	$62.8365	$62.84	$62.85	$62.80
Purchase #7	$137.31	13.675%	$156.0871	$156.09	$156.10	$156.10
7 purchase totals =	$1,145.75		$1,255.5867	$1,255.59	$1,255.65	$1,255.50