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	$151.30	13.323%	$171.4577	$171.46	$171.45	$171.50
Purchase #2	$71.85	12.708%	$80.9807	$80.98	$81.00	$81.00
Purchase #3	$10.55	7.168%	$11.3062	$11.31	$11.30	$11.30
Purchase #4	$20.59	4.537%	$21.5242	$21.52	$21.50	$21.50
Purchase #5	$245.55	7.706%	$264.4721	$264.47	$264.45	$264.50
Purchase #6	$191.75	9.709%	$210.367	$210.37	$210.35	$210.40
Purchase #7	$200.79	12.571%	$226.0313	$226.03	$226.05	$226.00
7 purchase totals =	$892.38		$986.1392	$986.14	$986.10	$986.20