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	$65.82	8.767%	$71.5904	$71.59	$71.60	$71.60
Purchase #2	$113.92	5.587%	$120.2847	$120.28	$120.30	$120.30
Purchase #3	$81.57	9.371%	$89.2139	$89.21	$89.20	$89.20
Purchase #4	$65.57	9.115%	$71.5467	$71.55	$71.55	$71.50
Purchase #5	$81.36	5.434%	$85.7811	$85.78	$85.80	$85.80
Purchase #6	$14.32	4.585%	$14.9766	$14.98	$15.00	$15.00
Purchase #7	$63.28	12.691%	$71.3109	$71.31	$71.30	$71.30
7 purchase totals =	$485.84		$524.7043	$524.70	$524.75	$524.70