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	$27.39	4.872%	$28.7244	$28.72	$28.70	$28.70
Purchase #2	$68.37	4.612%	$71.5232	$71.52	$71.50	$71.50
Purchase #3	$43.79	5.759%	$46.3119	$46.31	$46.30	$46.30
Purchase #4	$64.28	9.591%	$70.4451	$70.45	$70.45	$70.40
Purchase #5	$19.77	12.497%	$22.2407	$22.24	$22.25	$22.20
Purchase #6	$146.98	12.134%	$164.8146	$164.81	$164.80	$164.80
Purchase #7	$112.90	6.664%	$120.4237	$120.42	$120.40	$120.40
7 purchase totals =	$483.48		$524.4836	$524.47	$524.40	$524.30