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	$137.48	9.421%	$150.432	$150.43	$150.45	$150.40
Purchase #2	$114.61	13.605%	$130.2027	$130.20	$130.20	$130.20
Purchase #3	$40.82	6.140%	$43.3263	$43.33	$43.35	$43.30
Purchase #4	$159.77	8.159%	$172.8056	$172.81	$172.80	$172.80
Purchase #5	$187.97	9.299%	$205.4493	$205.45	$205.45	$205.40
Purchase #6	$65.32	3.421%	$67.5546	$67.55	$67.55	$67.60
Purchase #7	$31.55	12.259%	$35.4177	$35.42	$35.40	$35.40
7 purchase totals =	$737.52		$805.1882	$805.19	$805.20	$805.10