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	$50.51	3.146%	$52.099	$52.10	$52.10	$52.10
Purchase #2	$204.46	4.550%	$213.7629	$213.76	$213.75	$213.80
Purchase #3	$86.65	4.801%	$90.8101	$90.81	$90.80	$90.80
Purchase #4	$137.82	9.213%	$150.5174	$150.52	$150.50	$150.50
Purchase #5	$20.55	12.376%	$23.0933	$23.09	$23.10	$23.10
Purchase #6	$249.64	13.848%	$284.2101	$284.21	$284.20	$284.20
Purchase #7	$86.50	5.863%	$91.5715	$91.57	$91.55	$91.60
7 purchase totals =	$836.13		$906.0643	$906.06	$906.00	$906.10