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	$103.60	10.401%	$114.3754	$114.38	$114.40	$114.40
Purchase #2	$60.52	10.762%	$67.0332	$67.03	$67.05	$67.00
Purchase #3	$82.29	7.192%	$88.2083	$88.21	$88.20	$88.20
Purchase #4	$175.66	8.514%	$190.6157	$190.62	$190.60	$190.60
Purchase #5	$48.48	8.747%	$52.7205	$52.72	$52.70	$52.70
Purchase #6	$46.93	10.859%	$52.0261	$52.03	$52.05	$52.00
Purchase #7	$18.72	11.503%	$20.8734	$20.87	$20.85	$20.90
7 purchase totals =	$536.20		$585.8526	$585.86	$585.85	$585.80