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	$51.57	7.557%	$55.4671	$55.47	$55.45	$55.50
Purchase #2	$247.47	13.271%	$280.3117	$280.31	$280.30	$280.30
Purchase #3	$150.74	4.836%	$158.0298	$158.03	$158.05	$158.00
Purchase #4	$234.60	8.834%	$255.3246	$255.32	$255.30	$255.30
Purchase #5	$207.84	5.625%	$219.531	$219.53	$219.55	$219.50
Purchase #6	$228.88	7.613%	$246.3046	$246.30	$246.30	$246.30
Purchase #7	$85.28	8.526%	$92.551	$92.55	$92.55	$92.60
7 purchase totals =	$1,206.38		$1,307.5198	$1,307.51	$1,307.50	$1,307.50