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	$160.50	4.398%	$167.5588	$167.56	$167.55	$167.60
Purchase #2	$55.40	12.481%	$62.3145	$62.31	$62.30	$62.30
Purchase #3	$20.38	13.301%	$23.0907	$23.09	$23.10	$23.10
Purchase #4	$97.67	7.218%	$104.7198	$104.72	$104.70	$104.70
Purchase #5	$83.29	7.550%	$89.5784	$89.58	$89.60	$89.60
Purchase #6	$48.89	13.305%	$55.3948	$55.39	$55.40	$55.40
Purchase #7	$34.47	3.667%	$35.734	$35.73	$35.75	$35.70
7 purchase totals =	$500.60		$538.3910	$538.38	$538.40	$538.40