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	$200.40	7.567%	$215.5643	$215.56	$215.55	$215.60
Purchase #2	$237.48	11.511%	$264.8163	$264.82	$264.80	$264.80
Purchase #3	$92.50	12.477%	$104.0412	$104.04	$104.05	$104.00
Purchase #4	$151.75	6.467%	$161.5637	$161.56	$161.55	$161.60
Purchase #5	$239.83	10.389%	$264.7459	$264.75	$264.75	$264.70
Purchase #6	$105.55	9.390%	$115.4611	$115.46	$115.45	$115.50
Purchase #7	$162.31	12.384%	$182.4105	$182.41	$182.40	$182.40
7 purchase totals =	$1,189.82		$1,308.6030	$1,308.60	$1,308.55	$1,308.60