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	$8.59	7.249%	$9.2127	$9.21	$9.20	$9.20
Purchase #2	$202.57	10.151%	$223.1329	$223.13	$223.15	$223.10
Purchase #3	$52.33	4.300%	$54.5802	$54.58	$54.60	$54.60
Purchase #4	$135.34	9.498%	$148.1946	$148.19	$148.20	$148.20
Purchase #5	$132.40	9.528%	$145.0151	$145.02	$145.00	$145.00
Purchase #6	$85.56	6.195%	$90.8604	$90.86	$90.85	$90.90
Purchase #7	$81.57	10.872%	$90.4383	$90.44	$90.45	$90.40
7 purchase totals =	$698.36		$761.4342	$761.43	$761.45	$761.40