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	$41.95	8.244%	$45.4084	$45.41	$45.40	$45.40
Purchase #2	$51.48	6.616%	$54.8859	$54.89	$54.90	$54.90
Purchase #3	$235.36	9.183%	$256.9731	$256.97	$256.95	$257.00
Purchase #4	$241.96	12.627%	$272.5123	$272.51	$272.50	$272.50
Purchase #5	$35.85	7.214%	$38.4362	$38.44	$38.45	$38.40
Purchase #6	$96.77	13.509%	$109.8427	$109.84	$109.85	$109.80
Purchase #7	$33.63	12.240%	$37.7463	$37.75	$37.75	$37.70
7 purchase totals =	$737.00		$815.8049	$815.81	$815.80	$815.70