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	$25.82	11.779%	$28.8613	$28.86	$28.85	$28.90
Purchase #2	$88.47	11.340%	$98.5025	$98.50	$98.50	$98.50
Purchase #3	$150.72	6.553%	$160.5967	$160.60	$160.60	$160.60
Purchase #4	$47.89	13.142%	$54.1837	$54.18	$54.20	$54.20
Purchase #5	$29.43	12.302%	$33.0505	$33.05	$33.05	$33.10
Purchase #6	$166.52	12.209%	$186.8504	$186.85	$186.85	$186.90
Purchase #7	$226.46	13.109%	$256.1466	$256.15	$256.15	$256.10
7 purchase totals =	$735.31		$818.1917	$818.19	$818.20	$818.30