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	$142.45	11.184%	$158.3816	$158.38	$158.40	$158.40
Purchase #2	$226.64	8.265%	$245.3718	$245.37	$245.35	$245.40
Purchase #3	$29.48	12.458%	$33.1526	$33.15	$33.15	$33.20
Purchase #4	$28.46	13.366%	$32.264	$32.26	$32.25	$32.30
Purchase #5	$113.43	4.533%	$118.5718	$118.57	$118.55	$118.60
Purchase #6	$43.70	3.617%	$45.2806	$45.28	$45.30	$45.30
Purchase #7	$214.51	3.315%	$221.621	$221.62	$221.60	$221.60
7 purchase totals =	$798.67		$854.6434	$854.63	$854.60	$854.80