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	$108.94	11.296%	$121.2459	$121.25	$121.25	$121.20
Purchase #2	$87.26	4.170%	$90.8987	$90.90	$90.90	$90.90
Purchase #3	$73.86	13.816%	$84.0645	$84.06	$84.05	$84.10
Purchase #4	$55.50	9.668%	$60.8657	$60.87	$60.85	$60.90
Purchase #5	$85.78	4.501%	$89.641	$89.64	$89.65	$89.60
Purchase #6	$39.77	9.262%	$43.4535	$43.45	$43.45	$43.50
Purchase #7	$9.37	11.708%	$10.467	$10.47	$10.45	$10.50
7 purchase totals =	$460.48		$500.6363	$500.64	$500.60	$500.70