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	$19.37	8.621%	$21.0399	$21.04	$21.05	$21.00
Purchase #2	$118.27	4.700%	$123.8287	$123.83	$123.85	$123.80
Purchase #3	$228.81	7.364%	$245.6596	$245.66	$245.65	$245.70
Purchase #4	$42.73	3.696%	$44.3093	$44.31	$44.30	$44.30
Purchase #5	$52.25	4.323%	$54.5088	$54.51	$54.50	$54.50
Purchase #6	$217.73	4.704%	$227.972	$227.97	$227.95	$228.00
Purchase #7	$241.92	6.190%	$256.8948	$256.89	$256.90	$256.90
7 purchase totals =	$921.08		$974.2131	$974.21	$974.20	$974.20