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	$78.82	3.206%	$81.347	$81.35	$81.35	$81.30
Purchase #2	$42.38	12.139%	$47.5245	$47.52	$47.50	$47.50
Purchase #3	$158.48	3.856%	$164.591	$164.59	$164.60	$164.60
Purchase #4	$7.67	5.127%	$8.0632	$8.06	$8.05	$8.10
Purchase #5	$43.76	3.392%	$45.2443	$45.24	$45.25	$45.20
Purchase #6	$111.67	7.374%	$119.9045	$119.90	$119.90	$119.90
Purchase #7	$120.68	13.368%	$136.8125	$136.81	$136.80	$136.80
7 purchase totals =	$563.46		$603.4870	$603.47	$603.45	$603.40