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	$139.63	9.237%	$152.5276	$152.53	$152.55	$152.50
Purchase #2	$73.77	12.283%	$82.8312	$82.83	$82.85	$82.80
Purchase #3	$95.39	7.238%	$102.2943	$102.29	$102.30	$102.30
Purchase #4	$246.86	10.432%	$272.6124	$272.61	$272.60	$272.60
Purchase #5	$90.71	5.796%	$95.9676	$95.97	$95.95	$96.00
Purchase #6	$108.26	13.304%	$122.6629	$122.66	$122.65	$122.70
Purchase #7	$248.80	12.766%	$280.5618	$280.56	$280.55	$280.60
7 purchase totals =	$1,003.42		$1,109.4578	$1,109.45	$1,109.45	$1,109.50