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	$114.26	9.305%	$124.8919	$124.89	$124.90	$124.90
Purchase #2	$38.69	7.191%	$41.4722	$41.47	$41.45	$41.50
Purchase #3	$227.38	12.508%	$255.8207	$255.82	$255.80	$255.80
Purchase #4	$164.56	8.701%	$178.8784	$178.88	$178.90	$178.90
Purchase #5	$36.52	11.814%	$40.8345	$40.83	$40.85	$40.80
Purchase #6	$46.78	10.844%	$51.8528	$51.85	$51.85	$51.90
Purchase #7	$113.31	10.847%	$125.6007	$125.60	$125.60	$125.60
7 purchase totals =	$741.50		$819.3512	$819.34	$819.35	$819.40