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	$234.84	9.618%	$257.4269	$257.43	$257.45	$257.40
Purchase #2	$140.35	7.294%	$150.5871	$150.59	$150.60	$150.60
Purchase #3	$174.54	12.710%	$196.724	$196.72	$196.70	$196.70
Purchase #4	$13.59	7.662%	$14.6313	$14.63	$14.65	$14.60
Purchase #5	$209.51	9.732%	$229.8995	$229.90	$229.90	$229.90
Purchase #6	$73.75	10.417%	$81.4325	$81.43	$81.45	$81.40
Purchase #7	$66.81	3.307%	$69.0194	$69.02	$69.00	$69.00
7 purchase totals =	$913.39		$999.7207	$999.72	$999.75	$999.60