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	$181.47	3.829%	$188.4185	$188.42	$188.40	$188.40
Purchase #2	$214.56	10.660%	$237.4321	$237.43	$237.45	$237.40
Purchase #3	$35.30	9.706%	$38.7262	$38.73	$38.75	$38.70
Purchase #4	$21.96	13.410%	$24.9048	$24.90	$24.90	$24.90
Purchase #5	$86.79	4.282%	$90.5063	$90.51	$90.50	$90.50
Purchase #6	$223.36	7.196%	$239.433	$239.43	$239.45	$239.40
Purchase #7	$210.61	4.328%	$219.7252	$219.73	$219.75	$219.70
7 purchase totals =	$974.05		$1,039.1461	$1,039.15	$1,039.20	$1,039.00