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	$51.89	6.669%	$55.3505	$55.35	$55.35	$55.40
Purchase #2	$104.93	4.835%	$110.0034	$110.00	$110.00	$110.00
Purchase #3	$195.33	11.671%	$218.127	$218.13	$218.15	$218.10
Purchase #4	$10.39	9.682%	$11.396	$11.40	$11.40	$11.40
Purchase #5	$33.37	4.384%	$34.8329	$34.83	$34.85	$34.80
Purchase #6	$140.90	12.258%	$158.1715	$158.17	$158.15	$158.20
Purchase #7	$178.48	10.124%	$196.5493	$196.55	$196.55	$196.50
7 purchase totals =	$715.29		$784.4306	$784.43	$784.45	$784.40