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	$246.68	13.616%	$280.2679	$280.27	$280.25	$280.30
Purchase #2	$165.64	10.150%	$182.4525	$182.45	$182.45	$182.50
Purchase #3	$29.78	12.116%	$33.3881	$33.39	$33.40	$33.40
Purchase #4	$220.79	12.783%	$249.0136	$249.01	$249.00	$249.00
Purchase #5	$78.71	7.392%	$84.5282	$84.53	$84.55	$84.50
Purchase #6	$99.80	13.371%	$113.1443	$113.14	$113.15	$113.10
Purchase #7	$52.52	5.741%	$55.5352	$55.54	$55.55	$55.50
7 purchase totals =	$893.92		$998.3298	$998.33	$998.35	$998.30