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	$19.97	7.761%	$21.5199	$21.52	$21.50	$21.50
Purchase #2	$175.67	5.535%	$185.3933	$185.39	$185.40	$185.40
Purchase #3	$124.69	6.798%	$133.1664	$133.17	$133.15	$133.20
Purchase #4	$17.63	11.448%	$19.6483	$19.65	$19.65	$19.60
Purchase #5	$64.68	12.493%	$72.7605	$72.76	$72.75	$72.80
Purchase #6	$168.54	12.627%	$189.8215	$189.82	$189.80	$189.80
Purchase #7	$176.90	10.844%	$196.083	$196.08	$196.10	$196.10
7 purchase totals =	$748.08		$818.3929	$818.39	$818.35	$818.40