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	$119.77	12.696%	$134.976	$134.98	$135.00	$135.00
Purchase #2	$44.59	4.850%	$46.7526	$46.75	$46.75	$46.80
Purchase #3	$67.39	5.517%	$71.1079	$71.11	$71.10	$71.10
Purchase #4	$246.98	7.820%	$266.2938	$266.29	$266.30	$266.30
Purchase #5	$40.94	3.577%	$42.4044	$42.40	$42.40	$42.40
Purchase #6	$245.72	13.567%	$279.0568	$279.06	$279.05	$279.10
Purchase #7	$40.62	4.550%	$42.4682	$42.47	$42.45	$42.50
7 purchase totals =	$806.01		$883.0597	$883.06	$883.05	$883.20