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	$181.46	13.576%	$206.095	$206.10	$206.10	$206.10
Purchase #2	$187.63	4.701%	$196.4505	$196.45	$196.45	$196.50
Purchase #3	$229.36	11.543%	$255.835	$255.84	$255.85	$255.80
Purchase #4	$73.62	10.321%	$81.2183	$81.22	$81.20	$81.20
Purchase #5	$118.29	12.458%	$133.0266	$133.03	$133.05	$133.00
Purchase #6	$143.83	7.490%	$154.6029	$154.60	$154.60	$154.60
Purchase #7	$45.83	13.550%	$52.04	$52.04	$52.05	$52.00
7 purchase totals =	$980.02		$1,079.2683	$1,079.28	$1,079.30	$1,079.20