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	$133.77	4.308%	$139.5328	$139.53	$139.55	$139.50
Purchase #2	$75.95	6.321%	$80.7508	$80.75	$80.75	$80.80
Purchase #3	$139.55	13.640%	$158.5846	$158.58	$158.60	$158.60
Purchase #4	$194.40	11.711%	$217.1662	$217.17	$217.15	$217.20
Purchase #5	$131.93	9.375%	$144.2984	$144.30	$144.30	$144.30
Purchase #6	$63.67	8.848%	$69.3035	$69.30	$69.30	$69.30
Purchase #7	$109.45	8.360%	$118.6	$118.60	$118.60	$118.60
7 purchase totals =	$848.72		$928.2363	$928.23	$928.25	$928.30