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	$171.79	6.175%	$182.398	$182.40	$182.40	$182.40
Purchase #2	$139.26	10.767%	$154.2541	$154.25	$154.25	$154.30
Purchase #3	$53.51	12.788%	$60.3529	$60.35	$60.35	$60.40
Purchase #4	$72.47	8.851%	$78.8843	$78.88	$78.90	$78.90
Purchase #5	$225.82	3.627%	$234.0105	$234.01	$234.00	$234.00
Purchase #6	$228.83	7.113%	$245.1067	$245.11	$245.10	$245.10
Purchase #7	$231.72	12.143%	$259.8578	$259.86	$259.85	$259.90
7 purchase totals =	$1,123.40		$1,214.8643	$1,214.86	$1,214.85	$1,215.00