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	$240.73	9.389%	$263.3321	$263.33	$263.35	$263.30
Purchase #2	$132.93	5.870%	$140.733	$140.73	$140.75	$140.70
Purchase #3	$20.80	5.261%	$21.8943	$21.89	$21.90	$21.90
Purchase #4	$161.30	10.636%	$178.4559	$178.46	$178.45	$178.50
Purchase #5	$125.59	4.364%	$131.0707	$131.07	$131.05	$131.10
Purchase #6	$50.33	11.468%	$56.1018	$56.10	$56.10	$56.10
Purchase #7	$177.79	10.178%	$195.8855	$195.89	$195.90	$195.90
7 purchase totals =	$909.47		$987.4733	$987.47	$987.50	$987.50