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	$39.82	6.660%	$42.472	$42.47	$42.45	$42.50
Purchase #2	$98.39	11.159%	$109.3693	$109.37	$109.35	$109.40
Purchase #3	$155.43	3.379%	$160.682	$160.68	$160.70	$160.70
Purchase #4	$93.92	6.381%	$99.913	$99.91	$99.90	$99.90
Purchase #5	$50.25	7.659%	$54.0986	$54.10	$54.10	$54.10
Purchase #6	$237.49	10.528%	$262.4929	$262.49	$262.50	$262.50
Purchase #7	$18.48	6.495%	$19.6803	$19.68	$19.70	$19.70
7 purchase totals =	$693.78		$748.7081	$748.70	$748.70	$748.80