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	$213.70	4.782%	$223.9191	$223.92	$223.90	$223.90
Purchase #2	$130.94	7.381%	$140.6047	$140.60	$140.60	$140.60
Purchase #3	$125.52	4.841%	$131.5964	$131.60	$131.60	$131.60
Purchase #4	$47.47	12.444%	$53.3772	$53.38	$53.40	$53.40
Purchase #5	$219.29	13.521%	$248.9402	$248.94	$248.95	$248.90
Purchase #6	$97.50	7.729%	$105.0358	$105.04	$105.05	$105.00
Purchase #7	$15.51	8.858%	$16.8839	$16.88	$16.90	$16.90
7 purchase totals =	$849.93		$920.3573	$920.36	$920.40	$920.30