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	$87.81	4.835%	$92.0556	$92.06	$92.05	$92.10
Purchase #2	$52.26	6.810%	$55.8189	$55.82	$55.80	$55.80
Purchase #3	$188.50	6.537%	$200.8222	$200.82	$200.80	$200.80
Purchase #4	$115.35	4.481%	$120.5188	$120.52	$120.50	$120.50
Purchase #5	$36.74	10.449%	$40.579	$40.58	$40.60	$40.60
Purchase #6	$188.67	3.611%	$195.4829	$195.48	$195.50	$195.50
Purchase #7	$160.65	12.158%	$180.1818	$180.18	$180.20	$180.20
7 purchase totals =	$829.98		$885.4592	$885.46	$885.45	$885.50