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	12.712%	$30.8718	$30.87	$30.85	$30.90
Purchase #2	$148.50	7.425%	$159.5261	$159.53	$159.55	$159.50
Purchase #3	$20.69	5.743%	$21.8782	$21.88	$21.90	$21.90
Purchase #4	$101.93	12.717%	$114.8924	$114.89	$114.90	$114.90
Purchase #5	$62.97	4.216%	$65.6248	$65.62	$65.60	$65.60
Purchase #6	$70.25	11.536%	$78.354	$78.35	$78.35	$78.40
Purchase #7	$122.60	4.786%	$128.4676	$128.47	$128.45	$128.50
7 purchase totals =	$554.33		$599.6149	$599.61	$599.60	$599.70