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	$103.46	8.168%	$111.9106	$111.91	$111.90	$111.90
Purchase #2	$249.30	12.391%	$280.1908	$280.19	$280.20	$280.20
Purchase #3	$191.92	6.607%	$204.6002	$204.60	$204.60	$204.60
Purchase #4	$118.73	8.124%	$128.3756	$128.38	$128.40	$128.40
Purchase #5	$25.72	8.525%	$27.9126	$27.91	$27.90	$27.90
Purchase #6	$166.76	4.461%	$174.1992	$174.20	$174.20	$174.20
Purchase #7	$133.95	6.828%	$143.0961	$143.10	$143.10	$143.10
7 purchase totals =	$989.84		$1,070.2851	$1,070.29	$1,070.30	$1,070.30