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	$56.74	5.394%	$59.8006	$59.80	$59.80	$59.80
Purchase #2	$237.80	13.558%	$270.0409	$270.04	$270.05	$270.00
Purchase #3	$50.52	3.578%	$52.3276	$52.33	$52.35	$52.30
Purchase #4	$156.74	9.370%	$171.4265	$171.43	$171.45	$171.40
Purchase #5	$168.53	3.109%	$173.7696	$173.77	$173.75	$173.80
Purchase #6	$248.47	7.286%	$266.5735	$266.57	$266.55	$266.60
Purchase #7	$213.86	8.313%	$231.6382	$231.64	$231.65	$231.60
7 purchase totals =	$1,132.66		$1,225.5769	$1,225.58	$1,225.60	$1,225.50