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	$16.69	11.160%	$18.5526	$18.55	$18.55	$18.60
Purchase #2	$85.45	4.771%	$89.5268	$89.53	$89.55	$89.50
Purchase #3	$81.34	6.142%	$86.3359	$86.34	$86.35	$86.30
Purchase #4	$220.43	9.307%	$240.9454	$240.95	$240.95	$240.90
Purchase #5	$126.57	4.160%	$131.8353	$131.84	$131.85	$131.80
Purchase #6	$165.40	13.498%	$187.7257	$187.73	$187.75	$187.70
Purchase #7	$140.26	13.249%	$158.843	$158.84	$158.85	$158.80
7 purchase totals =	$836.14		$913.7647	$913.78	$913.85	$913.60