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	$222.32	8.185%	$240.5169	$240.52	$240.50	$240.50
Purchase #2	$67.50	5.667%	$71.3252	$71.33	$71.35	$71.30
Purchase #3	$35.53	11.177%	$39.5012	$39.50	$39.50	$39.50
Purchase #4	$65.76	5.491%	$69.3709	$69.37	$69.35	$69.40
Purchase #5	$223.25	8.333%	$241.8534	$241.85	$241.85	$241.90
Purchase #6	$20.60	9.199%	$22.495	$22.50	$22.50	$22.50
Purchase #7	$198.46	8.723%	$215.7717	$215.77	$215.75	$215.80
7 purchase totals =	$833.42		$900.8343	$900.84	$900.80	$900.90