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	$20.61	4.179%	$21.4713	$21.47	$21.45	$21.50
Purchase #2	$48.54	12.575%	$54.6439	$54.64	$54.65	$54.60
Purchase #3	$93.80	7.212%	$100.5649	$100.56	$100.55	$100.60
Purchase #4	$19.33	12.649%	$21.7751	$21.78	$21.80	$21.80
Purchase #5	$20.86	9.354%	$22.8112	$22.81	$22.80	$22.80
Purchase #6	$96.37	6.282%	$102.424	$102.42	$102.40	$102.40
Purchase #7	$194.41	5.438%	$204.982	$204.98	$205.00	$205.00
7 purchase totals =	$493.92		$528.6724	$528.66	$528.65	$528.70