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	$22.80	10.372%	$25.1648	$25.16	$25.15	$25.20
Purchase #2	$184.81	11.369%	$205.821	$205.82	$205.80	$205.80
Purchase #3	$15.59	11.588%	$17.3966	$17.40	$17.40	$17.40
Purchase #4	$51.53	6.530%	$54.8949	$54.89	$54.90	$54.90
Purchase #5	$133.86	4.442%	$139.8061	$139.81	$139.80	$139.80
Purchase #6	$67.82	4.369%	$70.7831	$70.78	$70.80	$70.80
Purchase #7	$20.89	4.377%	$21.8044	$21.80	$21.80	$21.80
7 purchase totals =	$497.30		$535.6709	$535.66	$535.65	$535.70