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	$132.29	11.463%	$147.4544	$147.45	$147.45	$147.50
Purchase #2	$248.34	3.446%	$256.8978	$256.90	$256.90	$256.90
Purchase #3	$45.98	12.274%	$51.6236	$51.62	$51.60	$51.60
Purchase #4	$127.45	7.527%	$137.0432	$137.04	$137.05	$137.00
Purchase #5	$218.48	9.540%	$239.323	$239.32	$239.30	$239.30
Purchase #6	$215.82	3.309%	$222.9615	$222.96	$222.95	$223.00
Purchase #7	$41.86	8.652%	$45.4817	$45.48	$45.50	$45.50
7 purchase totals =	$1,030.22		$1,100.7852	$1,100.77	$1,100.75	$1,100.80