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	$13.47	5.754%	$14.2451	$14.25	$14.25	$14.20
Purchase #2	$137.71	3.391%	$142.3797	$142.38	$142.40	$142.40
Purchase #3	$77.56	6.808%	$82.8403	$82.84	$82.85	$82.80
Purchase #4	$135.43	13.372%	$153.5397	$153.54	$153.55	$153.50
Purchase #5	$217.45	6.292%	$231.132	$231.13	$231.15	$231.10
Purchase #6	$131.54	8.856%	$143.1892	$143.19	$143.20	$143.20
Purchase #7	$62.80	13.847%	$71.4959	$71.50	$71.50	$71.50
7 purchase totals =	$775.96		$838.8219	$838.83	$838.90	$838.70