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	$200.57	13.112%	$226.8687	$226.87	$226.85	$226.90
Purchase #2	$207.42	7.859%	$223.7211	$223.72	$223.70	$223.70
Purchase #3	$237.35	7.853%	$255.9891	$255.99	$256.00	$256.00
Purchase #4	$202.88	12.647%	$228.5382	$228.54	$228.55	$228.50
Purchase #5	$73.69	11.832%	$82.409	$82.41	$82.40	$82.40
Purchase #6	$109.73	12.499%	$123.4452	$123.45	$123.45	$123.40
Purchase #7	$227.98	12.550%	$256.5915	$256.59	$256.60	$256.60
7 purchase totals =	$1,259.62		$1,397.5628	$1,397.57	$1,397.55	$1,397.50