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	$155.41	3.480%	$160.8183	$160.82	$160.80	$160.80
Purchase #2	$115.69	10.191%	$127.48	$127.48	$127.50	$127.50
Purchase #3	$93.94	10.481%	$103.7859	$103.79	$103.80	$103.80
Purchase #4	$156.56	13.431%	$177.5876	$177.59	$177.60	$177.60
Purchase #5	$16.50	8.514%	$17.9048	$17.90	$17.90	$17.90
Purchase #6	$139.45	8.629%	$151.4831	$151.48	$151.50	$151.50
Purchase #7	$237.57	10.724%	$263.047	$263.05	$263.05	$263.00
7 purchase totals =	$915.12		$1,002.1067	$1,002.11	$1,002.15	$1,002.10