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	$53.40	12.294%	$59.965	$59.97	$59.95	$60.00
Purchase #2	$130.34	9.609%	$142.8644	$142.86	$142.85	$142.90
Purchase #3	$64.59	6.334%	$68.6811	$68.68	$68.70	$68.70
Purchase #4	$142.99	11.546%	$159.4996	$159.50	$159.50	$159.50
Purchase #5	$95.67	8.621%	$103.9177	$103.92	$103.90	$103.90
Purchase #6	$187.25	10.469%	$206.8532	$206.85	$206.85	$206.90
Purchase #7	$82.29	3.622%	$85.2705	$85.27	$85.25	$85.30
7 purchase totals =	$756.53		$827.0515	$827.05	$827.00	$827.20