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	$21.55	3.705%	$22.3484	$22.35	$22.35	$22.30
Purchase #2	$149.96	13.599%	$170.3531	$170.35	$170.35	$170.40
Purchase #3	$123.87	10.783%	$137.2269	$137.23	$137.25	$137.20
Purchase #4	$82.93	9.601%	$90.8921	$90.89	$90.90	$90.90
Purchase #5	$196.96	12.435%	$221.452	$221.45	$221.45	$221.50
Purchase #6	$246.86	5.394%	$260.1756	$260.18	$260.20	$260.20
Purchase #7	$162.99	12.647%	$183.6033	$183.60	$183.60	$183.60
7 purchase totals =	$985.12		$1,086.0514	$1,086.05	$1,086.10	$1,086.10