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	$15.46	11.243%	$17.1982	$17.20	$17.20	$17.20
Purchase #2	$199.41	6.602%	$212.575	$212.58	$212.60	$212.60
Purchase #3	$62.89	4.765%	$65.8867	$65.89	$65.90	$65.90
Purchase #4	$11.36	11.521%	$12.6688	$12.67	$12.65	$12.70
Purchase #5	$171.80	6.127%	$182.3262	$182.33	$182.35	$182.30
Purchase #6	$47.80	7.757%	$51.5078	$51.51	$51.50	$51.50
Purchase #7	$65.32	10.848%	$72.4059	$72.41	$72.40	$72.40
7 purchase totals =	$574.04		$614.5686	$614.59	$614.60	$614.60