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	$89.32	12.481%	$100.468	$100.47	$100.45	$100.50
Purchase #2	$202.99	12.510%	$228.384	$228.38	$228.40	$228.40
Purchase #3	$237.36	7.601%	$255.4017	$255.40	$255.40	$255.40
Purchase #4	$173.46	12.124%	$194.4903	$194.49	$194.50	$194.50
Purchase #5	$33.53	6.279%	$35.6353	$35.64	$35.65	$35.60
Purchase #6	$146.89	7.783%	$158.3224	$158.32	$158.30	$158.30
Purchase #7	$241.82	3.746%	$250.8786	$250.88	$250.90	$250.90
7 purchase totals =	$1,125.37		$1,223.5803	$1,223.58	$1,223.60	$1,223.60