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	$52.56	7.339%	$56.4174	$56.42	$56.40	$56.40
Purchase #2	$243.69	6.497%	$259.5225	$259.52	$259.50	$259.50
Purchase #3	$117.91	4.680%	$123.4282	$123.43	$123.45	$123.40
Purchase #4	$95.55	6.557%	$101.8152	$101.82	$101.80	$101.80
Purchase #5	$213.84	8.177%	$231.3257	$231.33	$231.35	$231.30
Purchase #6	$124.61	11.741%	$139.2405	$139.24	$139.25	$139.20
Purchase #7	$50.95	8.626%	$55.3449	$55.34	$55.35	$55.30
7 purchase totals =	$899.11		$967.0944	$967.10	$967.10	$966.90